PSR J1311-3430: A Heavyweight Neutron Star with a Flyweight Helium Companion. (arXiv:1210.6884v1 [astro-ph.HE]):
We have obtained initial spectroscopic observations and additional photometry
of the newly discovered Pb=94min gamma-ray black-widow pulsar PSR J1311-3430.
The Keck spectra show a He-dominated, nearly H-free photosphere and a large
radial-velocity amplitude of 609.5+/-7.5km/s. Simultaneous seven-color GROND
photometry further probes the heating of this companion, and shows the presence
of a flaring infrared excess. We have modeled the quiescent light curve,
constraining the orbital inclination and masses. Simple heated light-curve fits
give M_NS=2.7Msun, but show systematic light-curve differences. Adding extra
components allows a larger mass range to be fit, but all viable solutions have
M_NS>2.1Msun. If confirmed, such a large M_NS substantially constrains the
equation of state of matter at supernuclear densities.
Saturday, October 27, 2012
X-ray variability of PMS stars - Toward an explanation of the different X-ray properties of CTTS and WTTS. (arXiv:1210.6770v1 [astro-ph.SR])
X-ray variability of PMS stars - Toward an explanation of the different X-ray properties of CTTS and WTTS. (arXiv:1210.6770v1 [astro-ph.SR]):
The intense X-ray emission from coronae and accretion shocks in young PMS
stars is likely to play an important role in the evolution and dispersal of
circumstellar disks. Several aspects of the physics of this X-ray emission
remain mysterious, e.g., whether and how much accretion affects coronal
emission.
We studied the X-ray variability of ~1 Myr old low-mass PMS stars as a
function of timescale, stellar rotation, and stellar characteristics, in order
to gain insights on the working of PMS coronae, their X-ray emission, and the
circumstellar environment in which they are immersed.
We have exploited the ~850 ksec long Chandra observation of the Orion Nebula
Cluster obtained by the COUP collaboration in Jan. 2003, and statistically
analyzed the X-ray lightcurves of low-mass stars in several subsamples. In
particular, we characterized the different X-ray behavior of stars with and
without circumstellar accretion disks.
Accreting stars (Classical T Tauri Stars, CTTSs) are found to be more
variable than non accreting ones (Weak-lined T Tauri Stars, WTTSs) at all
timescales and in all the X-ray energy bands considered. Variability is seen to
increase with time-scale up to $\sim$10 days, i.e. the longest probed.
Signatures of rotational modulation are observed for both CTTSs and WTTSs, and
most clearly for CTTSs in the soft X-ray band. Lower mass stars are more
variable than higher mass ones.
We propose that the difference in variability between CTTSs and WTTSs may be
explained assuming that the X-ray emission of CTTS is affected by time-variable
absorption due circumstellar structures, such as warps in the inner disk and/or
accretion streams. This suggestion is appealing because, in the hypothesis that
the coronae of CTTSs and WTTSs are similar, it may also explain why CTTSs have
lower and more scattered X-ray emission levels with respect to WTTSs.
The intense X-ray emission from coronae and accretion shocks in young PMS
stars is likely to play an important role in the evolution and dispersal of
circumstellar disks. Several aspects of the physics of this X-ray emission
remain mysterious, e.g., whether and how much accretion affects coronal
emission.
We studied the X-ray variability of ~1 Myr old low-mass PMS stars as a
function of timescale, stellar rotation, and stellar characteristics, in order
to gain insights on the working of PMS coronae, their X-ray emission, and the
circumstellar environment in which they are immersed.
We have exploited the ~850 ksec long Chandra observation of the Orion Nebula
Cluster obtained by the COUP collaboration in Jan. 2003, and statistically
analyzed the X-ray lightcurves of low-mass stars in several subsamples. In
particular, we characterized the different X-ray behavior of stars with and
without circumstellar accretion disks.
Accreting stars (Classical T Tauri Stars, CTTSs) are found to be more
variable than non accreting ones (Weak-lined T Tauri Stars, WTTSs) at all
timescales and in all the X-ray energy bands considered. Variability is seen to
increase with time-scale up to $\sim$10 days, i.e. the longest probed.
Signatures of rotational modulation are observed for both CTTSs and WTTSs, and
most clearly for CTTSs in the soft X-ray band. Lower mass stars are more
variable than higher mass ones.
We propose that the difference in variability between CTTSs and WTTSs may be
explained assuming that the X-ray emission of CTTS is affected by time-variable
absorption due circumstellar structures, such as warps in the inner disk and/or
accretion streams. This suggestion is appealing because, in the hypothesis that
the coronae of CTTSs and WTTSs are similar, it may also explain why CTTSs have
lower and more scattered X-ray emission levels with respect to WTTSs.
Quantifying properties of ICM inhomogeneities. (arXiv:1210.6706v1 [astro-ph.HE])
Quantifying properties of ICM inhomogeneities. (arXiv:1210.6706v1 [astro-ph.HE]):
We present a new method to identify and characterize the structure of the
intracluster medium (ICM) in simulated galaxy clusters. The method uses the
median of gas properties, such as density and pressure, which we show to be
very robust to the presence of gas inhomogeneities. In particular, we show that
the radial profiles of median gas properties are smooth and do not exhibit
fluctuations at locations of massive clumps in contrast to mean and mode
properties. It is shown that distribution of gas properties in a given radial
shell can be well described by a log-normal PDF and a tail. The former
corresponds to a nearly hydrostatic bulk component, accounting for ~99% of the
volume, while the tail corresponds to high density inhomogeneities. We show
that this results in a simple and robust separation of the diffuse and clumpy
components of the ICM. The FWHM of the density distribution grows with radius
and varies from ~0.15 dex in cluster centre to ~0.5 dex at 2r_500 in relaxed
clusters. The small scatter in the width between relaxed clusters suggests that
the degree of inhomogeneity is a robust characteristic of the ICM. It broadly
agrees with the amplitude of density perturbations in the Coma cluster. We
discuss the origin of ICM density variations in spherical shells and show that
less than 20% of the width can be attributed to the triaxiality of the cluster
gravitational potential. As a link to X-ray observations of real clusters we
evaluated the ICM clumping factor with and without high density
inhomogeneities. We argue that these two cases represent upper and lower limits
on the departure of the observed X-ray emissivity from the median value. We
find that the typical value of the clumping factor in the bulk component of
relaxed clusters varies from ~1.1-1.2 at r_500 up to ~1.3-1.4 at r_200, in
broad agreement with recent observations.
We present a new method to identify and characterize the structure of the
intracluster medium (ICM) in simulated galaxy clusters. The method uses the
median of gas properties, such as density and pressure, which we show to be
very robust to the presence of gas inhomogeneities. In particular, we show that
the radial profiles of median gas properties are smooth and do not exhibit
fluctuations at locations of massive clumps in contrast to mean and mode
properties. It is shown that distribution of gas properties in a given radial
shell can be well described by a log-normal PDF and a tail. The former
corresponds to a nearly hydrostatic bulk component, accounting for ~99% of the
volume, while the tail corresponds to high density inhomogeneities. We show
that this results in a simple and robust separation of the diffuse and clumpy
components of the ICM. The FWHM of the density distribution grows with radius
and varies from ~0.15 dex in cluster centre to ~0.5 dex at 2r_500 in relaxed
clusters. The small scatter in the width between relaxed clusters suggests that
the degree of inhomogeneity is a robust characteristic of the ICM. It broadly
agrees with the amplitude of density perturbations in the Coma cluster. We
discuss the origin of ICM density variations in spherical shells and show that
less than 20% of the width can be attributed to the triaxiality of the cluster
gravitational potential. As a link to X-ray observations of real clusters we
evaluated the ICM clumping factor with and without high density
inhomogeneities. We argue that these two cases represent upper and lower limits
on the departure of the observed X-ray emissivity from the median value. We
find that the typical value of the clumping factor in the bulk component of
relaxed clusters varies from ~1.1-1.2 at r_500 up to ~1.3-1.4 at r_200, in
broad agreement with recent observations.
Thursday, October 25, 2012
Cross-correlating cosmic IR and X-ray background fluctuations: evidence of significant black hole populations among the CIB sources. (arXiv:1210.5302v1 [astro-ph.CO])
Cross-correlating cosmic IR and X-ray background fluctuations: evidence of significant black hole populations among the CIB sources. (arXiv:1210.5302v1 [astro-ph.CO]):
In order to understand the nature of the sources producing the recently
uncovered CIB fluctuations, we study cross-correlations between the
fluctuations in the source-subtracted Cosmic Infrared Background (CIB) from
Spitzer/IRAC data and the unresolved Cosmic X-ray Background (CXB) from deep
Chandra observations. Our study uses data from the EGS/AEGIS field, where both
datasets cover an ~8'x45' region of the sky. Quantitatively, our measurement is
the cross-power spectrum between the IR and X-ray data which we detect to be
statistically significant and positive at angular scales >20" where the
source-subtracted CIB fluctuations in the Spitzer data are dominated by the
clustering component. The cross-power signal between the IRAC maps at 3.6 um
and 4.5 um and the Chandra [0.5-2] keV data has been detected with the overall
significance of ~3.5 sigma and ~5 sigma respectively. At the same time we find
no evidence of significant cross-correlations at the harder Chandra bands. The
cross-correlation signal is produced by individual IR sources with 3.6 um and
4.5 um magnitudes m_AB>25-26 and [0.5-2] keV X-ray fluxes <<7x10^-17 cgs. We
determine that at least 15-25% of the large scale power of CIB fluctuations is
correlated with the spatial power spectrum of the X-ray fluctuations. If this
correlation is attributed to emission from accretion processes at both IR and
X-ray wavelengths, this implies a much higher fraction of the accreting black
holes than among the known populations. We discuss the various possible low-
and high-z suspects for the discovered cross-power and show that neither local
foregrounds, nor the known remaining normal galaxies and active galactic nuclei
(AGN) can reproduce the measurements. These observational results are an
important new constraint on theoretical modeling of the near-IR CIB
fluctuations.
In order to understand the nature of the sources producing the recently
uncovered CIB fluctuations, we study cross-correlations between the
fluctuations in the source-subtracted Cosmic Infrared Background (CIB) from
Spitzer/IRAC data and the unresolved Cosmic X-ray Background (CXB) from deep
Chandra observations. Our study uses data from the EGS/AEGIS field, where both
datasets cover an ~8'x45' region of the sky. Quantitatively, our measurement is
the cross-power spectrum between the IR and X-ray data which we detect to be
statistically significant and positive at angular scales >20" where the
source-subtracted CIB fluctuations in the Spitzer data are dominated by the
clustering component. The cross-power signal between the IRAC maps at 3.6 um
and 4.5 um and the Chandra [0.5-2] keV data has been detected with the overall
significance of ~3.5 sigma and ~5 sigma respectively. At the same time we find
no evidence of significant cross-correlations at the harder Chandra bands. The
cross-correlation signal is produced by individual IR sources with 3.6 um and
4.5 um magnitudes m_AB>25-26 and [0.5-2] keV X-ray fluxes <<7x10^-17 cgs. We
determine that at least 15-25% of the large scale power of CIB fluctuations is
correlated with the spatial power spectrum of the X-ray fluctuations. If this
correlation is attributed to emission from accretion processes at both IR and
X-ray wavelengths, this implies a much higher fraction of the accreting black
holes than among the known populations. We discuss the various possible low-
and high-z suspects for the discovered cross-power and show that neither local
foregrounds, nor the known remaining normal galaxies and active galactic nuclei
(AGN) can reproduce the measurements. These observational results are an
important new constraint on theoretical modeling of the near-IR CIB
fluctuations.
A High-Energy Catalogue of Galactic Supernova Remnants and Pulsar Wind Nebulae. (arXiv:1210.5264v1 [astro-ph.GA])
A High-Energy Catalogue of Galactic Supernova Remnants and Pulsar Wind Nebulae. (arXiv:1210.5264v1 [astro-ph.GA]):
Motivated by the wealth of past, existing, and upcoming X-ray and gamma-ray
missions, we have developed the first public database of high-energy
observations of all known Galactic Supernova Remnants (SNRs):
this http URL The catalogue links to, and
complements, other existing related catalogues, including Dave Green's radio
SNRs catalogue. We here highlight the features of the high-energy catalogue,
including allowing users to filter or sort data for various purposes. The
catalogue is currently targeted to Galactic SNR observations with X-ray and
gamma-ray missions, and is timely with the upcoming launch of X-ray missions
(including Astro-H). We are currently developing the existing database to
include an up-to-date Pulsar Wind Nebulae (PWNe)-dedicated webpage, with the
goal to provide a global view of PWNe and their associated neutron
stars/pulsars. This extensive database will be useful to both theorists to
apply their models or design numerical simulations, and to observers to plan
future observations or design new instruments. We welcome input and feedback
from the SNR/PWN/neutron stars community.
Motivated by the wealth of past, existing, and upcoming X-ray and gamma-ray
missions, we have developed the first public database of high-energy
observations of all known Galactic Supernova Remnants (SNRs):
this http URL The catalogue links to, and
complements, other existing related catalogues, including Dave Green's radio
SNRs catalogue. We here highlight the features of the high-energy catalogue,
including allowing users to filter or sort data for various purposes. The
catalogue is currently targeted to Galactic SNR observations with X-ray and
gamma-ray missions, and is timely with the upcoming launch of X-ray missions
(including Astro-H). We are currently developing the existing database to
include an up-to-date Pulsar Wind Nebulae (PWNe)-dedicated webpage, with the
goal to provide a global view of PWNe and their associated neutron
stars/pulsars. This extensive database will be useful to both theorists to
apply their models or design numerical simulations, and to observers to plan
future observations or design new instruments. We welcome input and feedback
from the SNR/PWN/neutron stars community.
Order statistics applied to the most massive and most distant galaxy clusters. (arXiv:1210.6021v1 [astro-ph.CO])
Order statistics applied to the most massive and most distant galaxy clusters. (arXiv:1210.6021v1 [astro-ph.CO]):
In this work we present for the first time an analytic framework for
calculating the individual and joint distributions of the n-th most massive or
n-th highest redshift galaxy cluster for a given survey characteristic allowing
to formulate LCDM exclusion criteria. We show that the cumulative distribution
functions steepen with increasing order, giving them a higher constraining
power with respect to the extreme value statistics. Additionally, we find that
the order statistics in mass (being dominated by clusters at lower redshifts)
is sensitive to the matter density and the normalisation of the matter
fluctuations, whereas the order statistics in redshift is particularly
sensitive to the geometric evolution of the Universe. For a fixed cosmology,
both order statistics are efficient probes of the functional shape of the mass
function at the high mass end. To allow a quick assessment of both order
statistics, we provide fits as a function of the survey area that allow
percentile estimation with an accuracy better than two per cent. Furthermore,
we discuss the joint distributions in the two-dimensional case for different
combinations of order.
Having introduced the theory, we apply the order statistical analysis to the
SPT massive cluster sample and MCXC catalogue and find that the ten most
massive clusters in the sample are consistent with LCDM and the Tinker mass
function. In turn, by assuming the LCDM reference cosmology, order statistics
can also be utilised for consistency checks of the completeness of the observed
sample and of the modelling of the survey selection function. [abridged]
In this work we present for the first time an analytic framework for
calculating the individual and joint distributions of the n-th most massive or
n-th highest redshift galaxy cluster for a given survey characteristic allowing
to formulate LCDM exclusion criteria. We show that the cumulative distribution
functions steepen with increasing order, giving them a higher constraining
power with respect to the extreme value statistics. Additionally, we find that
the order statistics in mass (being dominated by clusters at lower redshifts)
is sensitive to the matter density and the normalisation of the matter
fluctuations, whereas the order statistics in redshift is particularly
sensitive to the geometric evolution of the Universe. For a fixed cosmology,
both order statistics are efficient probes of the functional shape of the mass
function at the high mass end. To allow a quick assessment of both order
statistics, we provide fits as a function of the survey area that allow
percentile estimation with an accuracy better than two per cent. Furthermore,
we discuss the joint distributions in the two-dimensional case for different
combinations of order.
Having introduced the theory, we apply the order statistical analysis to the
SPT massive cluster sample and MCXC catalogue and find that the ten most
massive clusters in the sample are consistent with LCDM and the Tinker mass
function. In turn, by assuming the LCDM reference cosmology, order statistics
can also be utilised for consistency checks of the completeness of the observed
sample and of the modelling of the survey selection function. [abridged]
A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates. (arXiv:1210.5679v1 [gr-qc])
A code to compute the emission of thin accretion disks in non-Kerr space-times and test the nature of black hole candidates. (arXiv:1210.5679v1 [gr-qc]):
Astrophysical black hole candidates are thought to be the Kerr black holes
predicted by General Relativity, but the actual nature of these objects has
still to be proven. The analysis of the electromagnetic radiation emitted by a
geometrically thin and optically thick accretion disk around a black hole
candidate can provide information about the geometry of the space-time around
the compact object and it can thus test the Kerr black hole hypothesis. In this
paper, I present a code based on a ray-tracing approach and capable of
computing some basic properties of thin accretion disks in space-times with
deviations from the Kerr background. The code can be used to fit current and
future X-ray data of stellar-mass black hole candidates and constrain possible
deviations from the Kerr geometry in the spin parameter-deformation parameter
plane.
Astrophysical black hole candidates are thought to be the Kerr black holes
predicted by General Relativity, but the actual nature of these objects has
still to be proven. The analysis of the electromagnetic radiation emitted by a
geometrically thin and optically thick accretion disk around a black hole
candidate can provide information about the geometry of the space-time around
the compact object and it can thus test the Kerr black hole hypothesis. In this
paper, I present a code based on a ray-tracing approach and capable of
computing some basic properties of thin accretion disks in space-times with
deviations from the Kerr background. The code can be used to fit current and
future X-ray data of stellar-mass black hole candidates and constrain possible
deviations from the Kerr geometry in the spin parameter-deformation parameter
plane.
Equations of State and Maximum Mass of Neutron Stars in Light of PSR J1614-2230. (arXiv:1210.5667v1 [astro-ph.SR])
Equations of State and Maximum Mass of Neutron Stars in Light of PSR J1614-2230. (arXiv:1210.5667v1 [astro-ph.SR]):
We shall examine various types of equations of state for neutron stars, which
determine the structure of neutron stars. In particular, the relation between
mass and radius of neutron stars is of primary consideration. By combining an
equation of state (EOS) with the Tolmann-Oppenheimer-Volkoff structure
equations, we can determine the theoretical maximum mass of a neutron star for
a given equation of state. One question we seek to answer is whether quark
matter can exist in the core of a neutron star. In light of the discovery of
pulsar PSR J1614-2230, the mass of which is observed to be 1.97 solar masses, a
valid equation of state must achieve a maximum mass that is greater than 2
solar masses. To try to solve this problem, we experiment with different sets
of parameters for the quark matter to try to meet the lower limit 2-solar-mass
criterion. It is found that certain parameters contribute significantly to the
maximum mass of a neutron star.
We shall examine various types of equations of state for neutron stars, which
determine the structure of neutron stars. In particular, the relation between
mass and radius of neutron stars is of primary consideration. By combining an
equation of state (EOS) with the Tolmann-Oppenheimer-Volkoff structure
equations, we can determine the theoretical maximum mass of a neutron star for
a given equation of state. One question we seek to answer is whether quark
matter can exist in the core of a neutron star. In light of the discovery of
pulsar PSR J1614-2230, the mass of which is observed to be 1.97 solar masses, a
valid equation of state must achieve a maximum mass that is greater than 2
solar masses. To try to solve this problem, we experiment with different sets
of parameters for the quark matter to try to meet the lower limit 2-solar-mass
criterion. It is found that certain parameters contribute significantly to the
maximum mass of a neutron star.
Cosmology with the largest galaxy cluster surveys: Going beyond Fisher matrix forecasts. (arXiv:1210.5586v1 [astro-ph.CO])
Cosmology with the largest galaxy cluster surveys: Going beyond Fisher matrix forecasts. (arXiv:1210.5586v1 [astro-ph.CO]):
We make the first detailed MCMC likelihood study of cosmological constraints
that are expected from some of the largest, ongoing and proposed, cluster
surveys in different wave-bands and compare the estimates to the prevalent
Fisher matrix forecasts. Mock catalogs of cluster counts expected from the
surveys -- eROSITA, WFXT, RCS2, DES and Planck, along with a mock dataset of
follow-up mass calibrations are analyzed for this purpose. A fair agreement
between MCMC and Fisher results is found only in the case of minimal models.
However, for many cases, the marginalized constraints obtained from Fisher and
MCMC methods can differ by factors of 30-100%. The discrepancy can be
alarmingly large for a time dependent dark energy equation of state, $w(a)$;
the Fisher methods are seen to under-estimate the constraints by as much as a
factor of 4--5. Typically, Fisher estimates become more and more inappropriate
as we move away from $\Lambda$CDM, to a constant-$w$ dark energy to varying-$w$
dark energy cosmologies. Fisher analysis, also, predicts incorrect parameter
degeneracies. From the point of mass-calibration uncertainties, a high value of
unknown scatter about the mean mass-observable relation, and its redshift
dependence, is seen to have large degeneracies with the cosmological parameters
$\sigma_8$ and $w(a)$ and can degrade the cosmological constraints
considerably. We find that the addition of mass-calibrated cluster datasets can
improve dark energy and $\sigma_8$ constraints by factors of 2--3 from what can
be obtained compared to CMB+SNe+BAO only. Since, details of future cluster
surveys are still being planned, we emphasize that optimal survey design must
be done using MCMC analysis rather than Fisher forecasting. (abridged)
We make the first detailed MCMC likelihood study of cosmological constraints
that are expected from some of the largest, ongoing and proposed, cluster
surveys in different wave-bands and compare the estimates to the prevalent
Fisher matrix forecasts. Mock catalogs of cluster counts expected from the
surveys -- eROSITA, WFXT, RCS2, DES and Planck, along with a mock dataset of
follow-up mass calibrations are analyzed for this purpose. A fair agreement
between MCMC and Fisher results is found only in the case of minimal models.
However, for many cases, the marginalized constraints obtained from Fisher and
MCMC methods can differ by factors of 30-100%. The discrepancy can be
alarmingly large for a time dependent dark energy equation of state, $w(a)$;
the Fisher methods are seen to under-estimate the constraints by as much as a
factor of 4--5. Typically, Fisher estimates become more and more inappropriate
as we move away from $\Lambda$CDM, to a constant-$w$ dark energy to varying-$w$
dark energy cosmologies. Fisher analysis, also, predicts incorrect parameter
degeneracies. From the point of mass-calibration uncertainties, a high value of
unknown scatter about the mean mass-observable relation, and its redshift
dependence, is seen to have large degeneracies with the cosmological parameters
$\sigma_8$ and $w(a)$ and can degrade the cosmological constraints
considerably. We find that the addition of mass-calibrated cluster datasets can
improve dark energy and $\sigma_8$ constraints by factors of 2--3 from what can
be obtained compared to CMB+SNe+BAO only. Since, details of future cluster
surveys are still being planned, we emphasize that optimal survey design must
be done using MCMC analysis rather than Fisher forecasting. (abridged)
Masses and Accretion Rates of Supermassive Black Holes in Active Galactic Nuclei from the INTEGRAL Survey. (arXiv:1210.6279v1 [astro-ph.CO])
Masses and Accretion Rates of Supermassive Black Holes in Active Galactic Nuclei from the INTEGRAL Survey. (arXiv:1210.6279v1 [astro-ph.CO]):
The masses of 68 supermassive black holes (SMBHs) in nearby (z<0.15) active
galactic nuclei (AGNs) detected by the INTEGRAL observatory in the hard X-ray
energy band (17-60 keV) outside the Galactic plane (|b| > 5 degrees) have been
estimated. Well-known relations between the SMBH mass and (1) the infrared
luminosity of the stellar bulge (from 2MASS data) and (2) the characteristics
of broad emission lines (from RTT-150 data) have been used. A comparison with
the more accurate SMBH mass estimates obtained by the reverberation-mapping
technique and from direct dynamical measurements is also made for several
objects. The SMBH masses derived from the correlation with the bulge luminosity
turn out to be systematically higher than the estimates made by other methods.
The ratio of the bolometric luminosity to the critical Eddington luminosity has
been found for all AGNs. It ranges from 1 to 100% for the overwhelming majority
of objects.
The masses of 68 supermassive black holes (SMBHs) in nearby (z<0.15) active
galactic nuclei (AGNs) detected by the INTEGRAL observatory in the hard X-ray
energy band (17-60 keV) outside the Galactic plane (|b| > 5 degrees) have been
estimated. Well-known relations between the SMBH mass and (1) the infrared
luminosity of the stellar bulge (from 2MASS data) and (2) the characteristics
of broad emission lines (from RTT-150 data) have been used. A comparison with
the more accurate SMBH mass estimates obtained by the reverberation-mapping
technique and from direct dynamical measurements is also made for several
objects. The SMBH masses derived from the correlation with the bulge luminosity
turn out to be systematically higher than the estimates made by other methods.
The ratio of the bolometric luminosity to the critical Eddington luminosity has
been found for all AGNs. It ranges from 1 to 100% for the overwhelming majority
of objects.
Accretion and outflow of gas in Markarian 509. (arXiv:1210.6245v1 [astro-ph.CO])
Accretion and outflow of gas in Markarian 509. (arXiv:1210.6245v1 [astro-ph.CO]):
A major uncertainty in models for photoionised outflows in AGN is the
distance of the gas to the central black hole. We present the results of a
massive multiwavelength monitoring campaign on the bright Seyfert 1 galaxy Mrk
509 to constrain the location of the outflow components dominating the soft
X-ray band.
Mrk 509 was monitored by XMM-Newton, Integral, Chandra, HST/COS and Swift in
2009. We have studied the response of the photoionised gas to the changes in
the ionising flux produced by the central regions. We were able to put tight
constraints on the variability of the absorbers from day to year time scales.
This allowed us to develop a model for the time-dependent photoionisation in
this source.
We find that the more highly ionised gas producing most X-ray line opacity is
at least 5 pc away from the core; upper limits to the distance of various
absorbing components range between 20 pc up to a few kpc. The more lowly
ionised gas producing most UV line opacity is at least 100 pc away from the
nucleus.
These results point to an origin of the dominant, slow (v<1000 km/s) outflow
components in the NLR or torus-region of Mrk 509. We find that while the
kinetic luminosity of the outflow is small, the mass carried away is likely
larger than the 0.5 Solar mass per year accreting onto the black hole.
We also determined the chemical composition of the outflow as well as
valuable constraints on the different emission regions. We find for instance
that the resolved component of the Fe-K line originates from a region 40-1000
gravitational radii from the black hole, and that the soft excess is produced
by Comptonisation in a warm (0.2-1 keV), optically thick (tau~10-20) corona
near the inner part of the disk.
A major uncertainty in models for photoionised outflows in AGN is the
distance of the gas to the central black hole. We present the results of a
massive multiwavelength monitoring campaign on the bright Seyfert 1 galaxy Mrk
509 to constrain the location of the outflow components dominating the soft
X-ray band.
Mrk 509 was monitored by XMM-Newton, Integral, Chandra, HST/COS and Swift in
2009. We have studied the response of the photoionised gas to the changes in
the ionising flux produced by the central regions. We were able to put tight
constraints on the variability of the absorbers from day to year time scales.
This allowed us to develop a model for the time-dependent photoionisation in
this source.
We find that the more highly ionised gas producing most X-ray line opacity is
at least 5 pc away from the core; upper limits to the distance of various
absorbing components range between 20 pc up to a few kpc. The more lowly
ionised gas producing most UV line opacity is at least 100 pc away from the
nucleus.
These results point to an origin of the dominant, slow (v<1000 km/s) outflow
components in the NLR or torus-region of Mrk 509. We find that while the
kinetic luminosity of the outflow is small, the mass carried away is likely
larger than the 0.5 Solar mass per year accreting onto the black hole.
We also determined the chemical composition of the outflow as well as
valuable constraints on the different emission regions. We find for instance
that the resolved component of the Fe-K line originates from a region 40-1000
gravitational radii from the black hole, and that the soft excess is produced
by Comptonisation in a warm (0.2-1 keV), optically thick (tau~10-20) corona
near the inner part of the disk.
Jet Launching Structure Resolved Near the Supermassive Black Hole in M87. (arXiv:1210.6132v1 [astro-ph.HE])
Jet Launching Structure Resolved Near the Supermassive Black Hole in M87. (arXiv:1210.6132v1 [astro-ph.HE]):
Approximately 10% of active galactic nuclei exhibit relativistic jets, which
are powered by accretion of matter onto super massive black holes. While the
measured width profiles of such jets on large scales agree with theories of
magnetic collimation, predicted structure on accretion disk scales at the jet
launch point has not been detected. We report radio interferometry observations
at 1.3mm wavelength of the elliptical galaxy M87 that spatially resolve the
base of the jet in this source. The derived size of 5.5 +/- 0.4 Schwarzschild
radii is significantly smaller than the innermost edge of a retrograde
accretion disk, suggesting that the M87 jet is powered by an accretion disk in
a prograde orbit around a spinning black hole.
Approximately 10% of active galactic nuclei exhibit relativistic jets, which
are powered by accretion of matter onto super massive black holes. While the
measured width profiles of such jets on large scales agree with theories of
magnetic collimation, predicted structure on accretion disk scales at the jet
launch point has not been detected. We report radio interferometry observations
at 1.3mm wavelength of the elliptical galaxy M87 that spatially resolve the
base of the jet in this source. The derived size of 5.5 +/- 0.4 Schwarzschild
radii is significantly smaller than the innermost edge of a retrograde
accretion disk, suggesting that the M87 jet is powered by an accretion disk in
a prograde orbit around a spinning black hole.
Theoretical Studies of Accretion of Matter onto White Dwarfs and the Single Degenerate Scenario for Supernovae of Type Ia. (arXiv:1210.6086v1 [astro-ph.SR])
Theoretical Studies of Accretion of Matter onto White Dwarfs and the Single Degenerate Scenario for Supernovae of Type Ia. (arXiv:1210.6086v1 [astro-ph.SR]):
We present a brief summary of the Single Degenerate Scenario for the
progenitors of Type Ia Supernovae in which it is assumed that a low mass
carbon-oxygen white dwarf is growing in mass as a result of accretion from a
secondary star in a close binary system. Recent hydrodynamic simulations of
accretion of solar material onto white dwarfs without mixing always produce a
thermonuclear runaway and steady burning does not occur. For a broad range in
WD mass (0.4 Solar masses to 1.35 Solar Masses), the maximum ejected material
occurs for the 1.25 Solar Mass sequences and then decreases as the white dwarf
mass decreases. Therefore, the white dwarfs are growing in mass as a
consequence of the accretion of solar material and as long as there is no
mixing of accreted material with core material. In contrast, a thermonuclear
runaway in the accreted hydrogen-rich layers on the low luminosity WDs in close
binary systems where mixing of core matter with accreted material has occurred
is the outburst mechanism for Classical, Recurrent, and Symbiotic novae. The
differences in characteristics of these systems is likely the WD mass and mass
accretion rate. The high levels of enrichment of CN ejecta in elements ranging
from carbon to sulfur confirm that there is dredge-up of matter from the core
of the WD and enable them to contribute to the chemical enrichment of the
interstellar medium. Therefore, studies of CNe can lead to an improved
understanding of Galactic nucleosynthesis, some sources of pre-solar grains,
and the Extragalactic distance scale. The characteristics of the outburst
depend on the white dwarf mass, luminosity, mass accretion rate, and the
chemical composition of both the accreting material and WD material. The
properties of the outburst also depends on when, how, and if the accreted
layers are mixed with the WD core and the mixing mechanism is still unknown.
We present a brief summary of the Single Degenerate Scenario for the
progenitors of Type Ia Supernovae in which it is assumed that a low mass
carbon-oxygen white dwarf is growing in mass as a result of accretion from a
secondary star in a close binary system. Recent hydrodynamic simulations of
accretion of solar material onto white dwarfs without mixing always produce a
thermonuclear runaway and steady burning does not occur. For a broad range in
WD mass (0.4 Solar masses to 1.35 Solar Masses), the maximum ejected material
occurs for the 1.25 Solar Mass sequences and then decreases as the white dwarf
mass decreases. Therefore, the white dwarfs are growing in mass as a
consequence of the accretion of solar material and as long as there is no
mixing of accreted material with core material. In contrast, a thermonuclear
runaway in the accreted hydrogen-rich layers on the low luminosity WDs in close
binary systems where mixing of core matter with accreted material has occurred
is the outburst mechanism for Classical, Recurrent, and Symbiotic novae. The
differences in characteristics of these systems is likely the WD mass and mass
accretion rate. The high levels of enrichment of CN ejecta in elements ranging
from carbon to sulfur confirm that there is dredge-up of matter from the core
of the WD and enable them to contribute to the chemical enrichment of the
interstellar medium. Therefore, studies of CNe can lead to an improved
understanding of Galactic nucleosynthesis, some sources of pre-solar grains,
and the Extragalactic distance scale. The characteristics of the outburst
depend on the white dwarf mass, luminosity, mass accretion rate, and the
chemical composition of both the accreting material and WD material. The
properties of the outburst also depends on when, how, and if the accreted
layers are mixed with the WD core and the mixing mechanism is still unknown.
EITHER keV sterile neutrinos OR quasi-degenerate active neutrinos. (arXiv:1210.6036v1 [hep-ph])
EITHER keV sterile neutrinos OR quasi-degenerate active neutrinos. (arXiv:1210.6036v1 [hep-ph]):
We present a No-Go theorem for keV sterile neutrino Dark Matter: if sterile
neutrinos at the keV scale play the role of Dark Matter, they are typically
unstable and their decay produces an astrophysical monoenergetic X-ray line. It
turns out that the observational bound on this line is so strong that it
contradicts the existence of a quasi-degenerate spectrum of active neutrinos in
a seesaw type I framework where the Casas-Ibarra matrix R is real. This is the
case in particular for models without CP violation. We give a general proof of
this theorem. While the theorem (like every No-Go theorem) relies on certain
assumptions, the situation under which it applies is still sufficiently general
to lead to interesting consequences for keV neutrino model building. In fact,
depending on the outcome of the next generation experiments, one might be able
to rule out whole classes of models for keV sterile neutrinos.
We present a No-Go theorem for keV sterile neutrino Dark Matter: if sterile
neutrinos at the keV scale play the role of Dark Matter, they are typically
unstable and their decay produces an astrophysical monoenergetic X-ray line. It
turns out that the observational bound on this line is so strong that it
contradicts the existence of a quasi-degenerate spectrum of active neutrinos in
a seesaw type I framework where the Casas-Ibarra matrix R is real. This is the
case in particular for models without CP violation. We give a general proof of
this theorem. While the theorem (like every No-Go theorem) relies on certain
assumptions, the situation under which it applies is still sufficiently general
to lead to interesting consequences for keV neutrino model building. In fact,
depending on the outcome of the next generation experiments, one might be able
to rule out whole classes of models for keV sterile neutrinos.
Spectrum of the unresolved cosmic X ray background: what is unresolved 50 years after its discovery. (arXiv:1210.6377v1 [astro-ph.CO])
Spectrum of the unresolved cosmic X ray background: what is unresolved 50 years after its discovery. (arXiv:1210.6377v1 [astro-ph.CO]):
We study the spectral properties of the unresolved cosmic X-ray background
(CXRB) in the 1.5-7.0 keV energy band with the aim of providing an
observational constraint on the statistical properties of those sources that
are too faint to be individually probed. We made use of the Swift X-ray
observation of the Chandra Deep Field South complemented by the Chandra data.
Exploiting the lowest instrument background (Swift) together with the deepest
observation ever performed (Chandra) we measured the unresolved emission at the
deepest level and with the best accuracy available today. We find that the
unresolved CXRB emission can be modeled by a single power law with a very hard
photon index Gamma=0.1+/-0.7 and a flux of 5(+/-3)E-12 cgs in the 2.0-10 keV
energy band (1 sigma error). Thanks to the low instrument background of the
Swift-XRT, we significantly improved the accuracy with respect to previous
measurements. These results point towards a novel ingredient in AGN population
synthesis models, namely a positive evolution of the Compton-thick AGN
population from local Universe to high redshift.
We study the spectral properties of the unresolved cosmic X-ray background
(CXRB) in the 1.5-7.0 keV energy band with the aim of providing an
observational constraint on the statistical properties of those sources that
are too faint to be individually probed. We made use of the Swift X-ray
observation of the Chandra Deep Field South complemented by the Chandra data.
Exploiting the lowest instrument background (Swift) together with the deepest
observation ever performed (Chandra) we measured the unresolved emission at the
deepest level and with the best accuracy available today. We find that the
unresolved CXRB emission can be modeled by a single power law with a very hard
photon index Gamma=0.1+/-0.7 and a flux of 5(+/-3)E-12 cgs in the 2.0-10 keV
energy band (1 sigma error). Thanks to the low instrument background of the
Swift-XRT, we significantly improved the accuracy with respect to previous
measurements. These results point towards a novel ingredient in AGN population
synthesis models, namely a positive evolution of the Compton-thick AGN
population from local Universe to high redshift.
Modeling Mid-Infrared Diagnostics of Obscured Quasars and Starbursts. (arXiv:1210.6347v1 [astro-ph.CO])
Modeling Mid-Infrared Diagnostics of Obscured Quasars and Starbursts. (arXiv:1210.6347v1 [astro-ph.CO]):
We analyze the link between active galactic nuclei (AGN) and mid-infrared
flux using dust radiative transfer calculations of starbursts realized in
hydrodynamical simulations. Focusing on the effect of galaxy dust, we evaluate
diagnostics commonly used to disentangle AGN and star formation in
ultraluminous infrared galaxies (ULIRGs). We examine these quantities as a
function of time, viewing angle, dust model, AGN spectrum, and AGN strength in
merger simulations meant to bracket the properties of ULIRGs. Our more obscured
starburst begins SF-dominated with significant PAH emission, and ends with a
~10^9 year period of red near-IR colors. At coalescence, when the AGN is most
luminous, dust obscures the near-infrared AGN signature, reduces the relative
emission from polycyclic aromatic hydrocarbons (PAHs), and enhances the 9.7
micron absorption by silicate grains. Although generally consistent with
previous interpretations, our results imply none of these indicators can
unambiguously estimate the AGN luminosity fraction in all cases. Some identify
relatively unobscured AGN where the direct torus emission is observed, while
others indicate more highly obscured AGN. We show that a combination of the
extinction feature at 9.7 microns, the PAH strength, and a near-infrared slope
can simultaneously constrain the AGN fraction and dust grain distribution for a
wide range of obscuration. We find that this procedure, accessible to the James
Webb Space Telescope, may estimate the AGN power as tightly as the hard X-ray
flux alone, thereby providing a valuable future cross-check and constraint for
large samples of distant ULIRGs.
We analyze the link between active galactic nuclei (AGN) and mid-infrared
flux using dust radiative transfer calculations of starbursts realized in
hydrodynamical simulations. Focusing on the effect of galaxy dust, we evaluate
diagnostics commonly used to disentangle AGN and star formation in
ultraluminous infrared galaxies (ULIRGs). We examine these quantities as a
function of time, viewing angle, dust model, AGN spectrum, and AGN strength in
merger simulations meant to bracket the properties of ULIRGs. Our more obscured
starburst begins SF-dominated with significant PAH emission, and ends with a
~10^9 year period of red near-IR colors. At coalescence, when the AGN is most
luminous, dust obscures the near-infrared AGN signature, reduces the relative
emission from polycyclic aromatic hydrocarbons (PAHs), and enhances the 9.7
micron absorption by silicate grains. Although generally consistent with
previous interpretations, our results imply none of these indicators can
unambiguously estimate the AGN luminosity fraction in all cases. Some identify
relatively unobscured AGN where the direct torus emission is observed, while
others indicate more highly obscured AGN. We show that a combination of the
extinction feature at 9.7 microns, the PAH strength, and a near-infrared slope
can simultaneously constrain the AGN fraction and dust grain distribution for a
wide range of obscuration. We find that this procedure, accessible to the James
Webb Space Telescope, may estimate the AGN power as tightly as the hard X-ray
flux alone, thereby providing a valuable future cross-check and constraint for
large samples of distant ULIRGs.
Thursday, October 18, 2012
Galaxy clusters as cosmological probes: the impact of baryonic physics. (arXiv:1210.4117v1 [astro-ph.CO])
Galaxy clusters as cosmological probes: the impact of baryonic physics. (arXiv:1210.4117v1 [astro-ph.CO]):
The halo mass function from N-body simulations of collisionless matter is
generally used to retrieve cosmological parameters from observed counts of
galaxy clusters. This neglects the observational fact that the baryonic mass
fraction in clusters is a random variable that, on average, increases with the
total mass. Considering a mock catalog that includes tens of thousands of
galaxy clusters, as expected from the forthcoming generation of surveys, we
show that the effect of a varying baryonic mass fraction will be observable
with high statistical significance. The net effect is a change in the overall
normalization of the cluster mass function and a milder modification of its
shape. Our results indicate the absolute necessity of taking into account
baryonic corrections to the mass function if one wants to obtain unbiased
estimates of the cosmological parameters from data of this quality. We
introduce the formalism necessary to accomplish this goal. Our discussion is
based on the conditional probability of finding a given value of the baryonic
mass fraction for clusters of fixed total mass. Finally, we show that combining
information from the cluster counts with measurements of the baryonic mass
fraction in a small subsample of clusters (including only a few tens of
objects) will nearly optimally constrain the cosmological parameters.
The halo mass function from N-body simulations of collisionless matter is
generally used to retrieve cosmological parameters from observed counts of
galaxy clusters. This neglects the observational fact that the baryonic mass
fraction in clusters is a random variable that, on average, increases with the
total mass. Considering a mock catalog that includes tens of thousands of
galaxy clusters, as expected from the forthcoming generation of surveys, we
show that the effect of a varying baryonic mass fraction will be observable
with high statistical significance. The net effect is a change in the overall
normalization of the cluster mass function and a milder modification of its
shape. Our results indicate the absolute necessity of taking into account
baryonic corrections to the mass function if one wants to obtain unbiased
estimates of the cosmological parameters from data of this quality. We
introduce the formalism necessary to accomplish this goal. Our discussion is
based on the conditional probability of finding a given value of the baryonic
mass fraction for clusters of fixed total mass. Finally, we show that combining
information from the cluster counts with measurements of the baryonic mass
fraction in a small subsample of clusters (including only a few tens of
objects) will nearly optimally constrain the cosmological parameters.
The Atacama Cosmology Telescope: Physical Properties of Sunyaev-Zel'dovich Effect Clusters on the Celestial Equator. (arXiv:1210.4048v1 [astro-ph.CO])
The Atacama Cosmology Telescope: Physical Properties of Sunyaev-Zel'dovich Effect Clusters on the Celestial Equator. (arXiv:1210.4048v1 [astro-ph.CO]):
We present the optical and X-ray properties of 68 galaxy clusters selected
via the Sunyaev-Zel'dovich Effect at 148 GHz by the Atacama Cosmology Telescope
(ACT). Our sample, from an area of 504 square degrees centered on the celestial
equator, is divided into two regions. The main region uses 270 square degrees
of the ACT survey that overlaps with the co-added ugriz imaging from the Sloan
Digital Sky Survey (SDSS) over Stripe 82 plus additional near-infrared pointed
observations with the Apache Point Observatory 3.5-meter telescope. We confirm
a total of 49 clusters to z~1.3, of which 22 (all at z>0.55) are new
discoveries. For the second region the regular-depth SDSS imaging allows us to
confirm 19 more clusters up to z~0.7, of which 10 systems are new. We present
the optical richness, photometric redshifts, and separation between the SZ
position and the brightest cluster galaxy (BCG). We find no significant offset
between the cluster SZ centroid and BCG location and a weak correlation between
optical richness and SZ-derived mass. We also present X-ray fluxes and
luminosities from the ROSAT All Sky Survey which confirm that this is a massive
sample. One of the newly discovered clusters, ACT-CL J0044.4+0113 at z=1.1
(photometric), has an integrated XMM-Newton X-ray temperature of kT_x=7.9+/-1.0
keV and combined mass of M_200a=8.2(-2.5,+3.3)x10^14 M_sun/h70 placing it among
the most massive and X-ray-hot clusters known at redshifts beyond z=1. We also
highlight the optically-rich cluster ACT-CL J2327.4-0204 (RCS2 2327) at z=0.705
(spectroscopic) as the most significant detection of the whole equatorial
sample with a Chandra-derived mass of M_200a=1.9(-0.4,+0.6)x10^15 M_sun/h70,
comparable to some of the most massive known clusters like "El Gordo" and the
Bullet Cluster.
We present the optical and X-ray properties of 68 galaxy clusters selected
via the Sunyaev-Zel'dovich Effect at 148 GHz by the Atacama Cosmology Telescope
(ACT). Our sample, from an area of 504 square degrees centered on the celestial
equator, is divided into two regions. The main region uses 270 square degrees
of the ACT survey that overlaps with the co-added ugriz imaging from the Sloan
Digital Sky Survey (SDSS) over Stripe 82 plus additional near-infrared pointed
observations with the Apache Point Observatory 3.5-meter telescope. We confirm
a total of 49 clusters to z~1.3, of which 22 (all at z>0.55) are new
discoveries. For the second region the regular-depth SDSS imaging allows us to
confirm 19 more clusters up to z~0.7, of which 10 systems are new. We present
the optical richness, photometric redshifts, and separation between the SZ
position and the brightest cluster galaxy (BCG). We find no significant offset
between the cluster SZ centroid and BCG location and a weak correlation between
optical richness and SZ-derived mass. We also present X-ray fluxes and
luminosities from the ROSAT All Sky Survey which confirm that this is a massive
sample. One of the newly discovered clusters, ACT-CL J0044.4+0113 at z=1.1
(photometric), has an integrated XMM-Newton X-ray temperature of kT_x=7.9+/-1.0
keV and combined mass of M_200a=8.2(-2.5,+3.3)x10^14 M_sun/h70 placing it among
the most massive and X-ray-hot clusters known at redshifts beyond z=1. We also
highlight the optically-rich cluster ACT-CL J2327.4-0204 (RCS2 2327) at z=0.705
(spectroscopic) as the most significant detection of the whole equatorial
sample with a Chandra-derived mass of M_200a=1.9(-0.4,+0.6)x10^15 M_sun/h70,
comparable to some of the most massive known clusters like "El Gordo" and the
Bullet Cluster.
The XMM-Newton slew survey in the 2-10 keV band. (arXiv:1210.3992v1 [astro-ph.CO])
The XMM-Newton slew survey in the 2-10 keV band. (arXiv:1210.3992v1 [astro-ph.CO]):
The XMM-Newton Slew Survey (XSS) covers a significant fraction of the sky in
a broad X-ray bandpass. Although shallow by contemporary standards, in the
`classical' 2-10 keV band of X-ray astronomy, the XSS provides significantly
better sensitivity than any currently available all-sky survey. We investigate
the source content of the XSS, focussing on detections in the 2-10 keV band
down to a very low threshold (> 4 counts net of background). At the faint end,
the survey reaches a flux sensitivity of roughly 3e-12 erg/cm2/s (2-10 keV).
Our starting point was a sample of 487 sources detected in the XMMSL1d2 XSS at
high galactic latitude in the hard band. Through cross-correlation with
published source catalogues from surveys spanning the electromagnetic spectrum
from radio to gamma-rays, we find that 45% of the sources have likely
identifications with normal/active galaxies, 18% are associated with other
classes of X-ray object (nearby coronally active stars, accreting binaries,
clusters of galaxies), leaving 37% of the XSS sources with no current
identification. We go on to define an XSS extragalactic hard band sample
comprised of 219 galaxies and active galaxies. We investigate the properties of
this extragalactic sample including its X-ray logN-logS distribution. We find
that in the low-count limit, the XSS is strongly affected by Eddington bias.
There is also a very strong bias in the XSS against the detection of extended
sources, most notably clusters of galaxies. A significant fraction of the
detections at and around the low-count limit may be spurious. Nevertheless, it
is possible to use the XSS to extract a reasonably robust sample of
extragalactic sources, excluding galaxy clusters. The differential logN-logS
relation of these extragalactic sources matches very well to the HEAO-1 A2
all-sky survey measurements at bright fluxes and to the 2XMM source counts at
the faint end.
The XMM-Newton Slew Survey (XSS) covers a significant fraction of the sky in
a broad X-ray bandpass. Although shallow by contemporary standards, in the
`classical' 2-10 keV band of X-ray astronomy, the XSS provides significantly
better sensitivity than any currently available all-sky survey. We investigate
the source content of the XSS, focussing on detections in the 2-10 keV band
down to a very low threshold (> 4 counts net of background). At the faint end,
the survey reaches a flux sensitivity of roughly 3e-12 erg/cm2/s (2-10 keV).
Our starting point was a sample of 487 sources detected in the XMMSL1d2 XSS at
high galactic latitude in the hard band. Through cross-correlation with
published source catalogues from surveys spanning the electromagnetic spectrum
from radio to gamma-rays, we find that 45% of the sources have likely
identifications with normal/active galaxies, 18% are associated with other
classes of X-ray object (nearby coronally active stars, accreting binaries,
clusters of galaxies), leaving 37% of the XSS sources with no current
identification. We go on to define an XSS extragalactic hard band sample
comprised of 219 galaxies and active galaxies. We investigate the properties of
this extragalactic sample including its X-ray logN-logS distribution. We find
that in the low-count limit, the XSS is strongly affected by Eddington bias.
There is also a very strong bias in the XSS against the detection of extended
sources, most notably clusters of galaxies. A significant fraction of the
detections at and around the low-count limit may be spurious. Nevertheless, it
is possible to use the XSS to extract a reasonably robust sample of
extragalactic sources, excluding galaxy clusters. The differential logN-logS
relation of these extragalactic sources matches very well to the HEAO-1 A2
all-sky survey measurements at bright fluxes and to the 2XMM source counts at
the faint end.
Black Holes in Ultra-Luminous X-ray sources: X-ray timing versus spectroscopy. (arXiv:1210.3965v1 [astro-ph.HE])
Black Holes in Ultra-Luminous X-ray sources: X-ray timing versus spectroscopy. (arXiv:1210.3965v1 [astro-ph.HE]):
Ultra-Luminous X-ray sources are accreting black holes that might represent
strong evidence of the Intermediate Mass Black Holes (IMBH), proposed to exist
by theoretical studies but with no firm detection (as a class) so far. We
analyze the best X-ray timing and spectral data from the ULX in NGC 5408
provided by XMM-Newton. The main goal is to study the broad-band noise
variability of the source. We found an anti-correlation of the fractional
root-mean square variability versus the intensity of the source, similar to
black-hole binaries during hard states.
Ultra-Luminous X-ray sources are accreting black holes that might represent
strong evidence of the Intermediate Mass Black Holes (IMBH), proposed to exist
by theoretical studies but with no firm detection (as a class) so far. We
analyze the best X-ray timing and spectral data from the ULX in NGC 5408
provided by XMM-Newton. The main goal is to study the broad-band noise
variability of the source. We found an anti-correlation of the fractional
root-mean square variability versus the intensity of the source, similar to
black-hole binaries during hard states.
The effects of strong magnetic fields on the neutron star structure: lowest order constrained variational calculations. (arXiv:1210.3690v1 [astro-ph.SR])
The effects of strong magnetic fields on the neutron star structure: lowest order constrained variational calculations. (arXiv:1210.3690v1 [astro-ph.SR]):
We investigate the effects of strong magnetic fields upon the gross
properties of neutron and protoneutron stars. In our calculations, the neutron
star matter was approximated by the pure neutron matter. Using the lowest order
constrained variational approach at zero and finite temperatures, and employing
$AV_{18}$ potential, we present the effects of strong magnetic fields on the
gravitational mass, radius, and gravitational redshift of the neutron and
protoneutron stars. It is found that the equation of state of neutron star
becomes stiffer with increase of the magnetic field and temperature. This leads
to larger values of the maximum mass and radius for the neutron stars.
We investigate the effects of strong magnetic fields upon the gross
properties of neutron and protoneutron stars. In our calculations, the neutron
star matter was approximated by the pure neutron matter. Using the lowest order
constrained variational approach at zero and finite temperatures, and employing
$AV_{18}$ potential, we present the effects of strong magnetic fields on the
gravitational mass, radius, and gravitational redshift of the neutron and
protoneutron stars. It is found that the equation of state of neutron star
becomes stiffer with increase of the magnetic field and temperature. This leads
to larger values of the maximum mass and radius for the neutron stars.
Joint Analysis of Cluster Observations: II. Chandra/XMM-Newton X-ray and Weak Lensing Scaling Relations for a Sample of 50 Rich Clusters of Galaxies. (arXiv:1210.3689v1 [astro-ph.CO])
Joint Analysis of Cluster Observations: II. Chandra/XMM-Newton X-ray and Weak Lensing Scaling Relations for a Sample of 50 Rich Clusters of Galaxies. (arXiv:1210.3689v1 [astro-ph.CO]):
We present a study of multiwavelength X-ray and weak lensing scaling
relations for a sample of 50 clusters of galaxies. Our analysis combines
Chandra and XMM-Newton data using an energy-dependent cross-calibration. After
considering a number of scaling relations, we find that gas mass is the most
robust estimator of weak lensing mass, yielding 15 +/- 6% intrinsic scatter at
r500. The scatter does not change when measured within a fixed physical radius
of 1 Mpc. Clusters with small BCG to X-ray peak offsets constitute a very
regular population whose members have the same gas mass fractions and whose
even smaller <10% deviations from regularity can be ascribed to line of sight
geometrical effects alone. Cool-core clusters, while a somewhat different
population, also show the same (<10%) scatter in the gas mass-lensing mass
relation. There is a good correlation and a hint of bimodality in the plane
defined by BCG offset and central entropy (or central cooling time). The
pseudo-pressure YX does not discriminate between the more relaxed and less
relaxed populations, making it perhaps the more even-handed mass proxy for
surveys. Overall, hydrostatic masses underestimate weak lensing masses by 10%
on the average at r500; but cool-core clusters are consistent with no bias,
while non-cool-core clusters have a large and constant 15-20% bias between
r2500 and r500, in agreement with N-body simulations incorporating
unthermalized gas. For non-cool-core clusters, the bias correlates well with
BCG ellipticity. We also examine centroid shift variance and and power ratios
to quantify substructure; these quantities do not correlate with residuals in
the scaling relations. Individual clusters have for the most part forgotten the
source of their departures from self-similarity.
We present a study of multiwavelength X-ray and weak lensing scaling
relations for a sample of 50 clusters of galaxies. Our analysis combines
Chandra and XMM-Newton data using an energy-dependent cross-calibration. After
considering a number of scaling relations, we find that gas mass is the most
robust estimator of weak lensing mass, yielding 15 +/- 6% intrinsic scatter at
r500. The scatter does not change when measured within a fixed physical radius
of 1 Mpc. Clusters with small BCG to X-ray peak offsets constitute a very
regular population whose members have the same gas mass fractions and whose
even smaller <10% deviations from regularity can be ascribed to line of sight
geometrical effects alone. Cool-core clusters, while a somewhat different
population, also show the same (<10%) scatter in the gas mass-lensing mass
relation. There is a good correlation and a hint of bimodality in the plane
defined by BCG offset and central entropy (or central cooling time). The
pseudo-pressure YX does not discriminate between the more relaxed and less
relaxed populations, making it perhaps the more even-handed mass proxy for
surveys. Overall, hydrostatic masses underestimate weak lensing masses by 10%
on the average at r500; but cool-core clusters are consistent with no bias,
while non-cool-core clusters have a large and constant 15-20% bias between
r2500 and r500, in agreement with N-body simulations incorporating
unthermalized gas. For non-cool-core clusters, the bias correlates well with
BCG ellipticity. We also examine centroid shift variance and and power ratios
to quantify substructure; these quantities do not correlate with residuals in
the scaling relations. Individual clusters have for the most part forgotten the
source of their departures from self-similarity.
The ASTRO-H X-ray Observatory. (arXiv:1210.4378v1 [astro-ph.IM])
The ASTRO-H X-ray Observatory. (arXiv:1210.4378v1 [astro-ph.IM]):
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly
successful X-ray missions initiated by the Institute of Space and Astronautical
Science (ISAS). ASTRO-H will investigate the physics of the high-energy
universe via a suite of four instruments, covering a very wide energy range,
from 0.3 keV to 600 keV. These instruments include a high-resolution,
high-throughput spectrometer sensitive over 0.3-2 keV with high spectral
resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in
the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers
covering 5-80 keV, located in the focal plane of multilayer-coated, focusing
hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12
keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and
a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the
40-600 keV band. The simultaneous broad bandpass, coupled with high spectral
resolution, will enable the pursuit of a wide variety of important science
themes.
The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly
successful X-ray missions initiated by the Institute of Space and Astronautical
Science (ISAS). ASTRO-H will investigate the physics of the high-energy
universe via a suite of four instruments, covering a very wide energy range,
from 0.3 keV to 600 keV. These instruments include a high-resolution,
high-throughput spectrometer sensitive over 0.3-2 keV with high spectral
resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in
the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers
covering 5-80 keV, located in the focal plane of multilayer-coated, focusing
hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12
keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and
a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the
40-600 keV band. The simultaneous broad bandpass, coupled with high spectral
resolution, will enable the pursuit of a wide variety of important science
themes.
A Consistent Approach to Falsifying Lambda-CDM with Rare Galaxy Clusters. (arXiv:1210.4369v1 [astro-ph.CO])
A Consistent Approach to Falsifying Lambda-CDM with Rare Galaxy Clusters. (arXiv:1210.4369v1 [astro-ph.CO]):
We consider methods with which to answer the question "is any observed galaxy
cluster too unusual for Lambda-CDM?" After emphasising that many previous
attempts to answer this question have fallen foul of a statistical bias which
causes them to overestimate the confidence levels to which Lambda-CDM can be
ruled out, we outline a consistent approach to these rare clusters which allows
the question to be answered. We explicitly separate the two procedures of first
ranking clusters according to which appears 'most unusual' and secondly
calculating the probability that such an unusual observation was made in a
given cosmology. For the ranking procedure we define three properties of
individual galaxy clusters, each of which are sensitive to changes in cluster
populations arising from different modifications to the cosmological model. We
use these properties to define the "equivalent mass at redshift zero" for a
cluster - the mass of an equally unusual cluster today. This quantity is
independent of the observational survey in which the cluster was found, which
makes it an ideal proxy for ranking the relative unusualness of clusters
detected by different surveys. We then calculate the probability that any
cluster could have been observed with this equivalent mass at redshift zero,
avoiding the a posteriori bias present in many earlier analyses. These two
steps are performed for a systematic and comprehensive sample of observed
galaxy clusters and we confirm that none are more than 1-sigma deviations from
the Lambda-CDM expectation. Whereas we have only applied our method to galaxy
clusters, it is applicable to any isolated, collapsed, halo. As motivation for
future surveys, we also calculate where in the mass redshift plane the rarest
halo is most likely to be found, giving information as to which objects might
be the most fruitful in the search for new physics.
We consider methods with which to answer the question "is any observed galaxy
cluster too unusual for Lambda-CDM?" After emphasising that many previous
attempts to answer this question have fallen foul of a statistical bias which
causes them to overestimate the confidence levels to which Lambda-CDM can be
ruled out, we outline a consistent approach to these rare clusters which allows
the question to be answered. We explicitly separate the two procedures of first
ranking clusters according to which appears 'most unusual' and secondly
calculating the probability that such an unusual observation was made in a
given cosmology. For the ranking procedure we define three properties of
individual galaxy clusters, each of which are sensitive to changes in cluster
populations arising from different modifications to the cosmological model. We
use these properties to define the "equivalent mass at redshift zero" for a
cluster - the mass of an equally unusual cluster today. This quantity is
independent of the observational survey in which the cluster was found, which
makes it an ideal proxy for ranking the relative unusualness of clusters
detected by different surveys. We then calculate the probability that any
cluster could have been observed with this equivalent mass at redshift zero,
avoiding the a posteriori bias present in many earlier analyses. These two
steps are performed for a systematic and comprehensive sample of observed
galaxy clusters and we confirm that none are more than 1-sigma deviations from
the Lambda-CDM expectation. Whereas we have only applied our method to galaxy
clusters, it is applicable to any isolated, collapsed, halo. As motivation for
future surveys, we also calculate where in the mass redshift plane the rarest
halo is most likely to be found, giving information as to which objects might
be the most fruitful in the search for new physics.
X-ray stacking of Lyman break galaxies in the 4\,Ms CDF-S - X-ray luminosities and star formation rates across cosmic time. (arXiv:1210.4188v1 [astro-ph.CO])
X-ray stacking of Lyman break galaxies in the 4\,Ms CDF-S - X-ray luminosities and star formation rates across cosmic time. (arXiv:1210.4188v1 [astro-ph.CO]):
Lyman Break Galaxies (LBGs) are widely thought to be prototypical young
galaxies in the early universe, particularly representative of those undergoing
massive events of star formation. Therefore, LBGs should produce significant
amounts of X-ray emission. We aim to trace the X-ray luminosity of Lyman Break
Galaxies across cosmic time and from that derive constraints on their star
formation history. We utilize the newly released 4 Ms mosaic obtained with the
Chandra X-ray Observatory, the deepest X-ray image to date, alongside with the
superb spectroscopic data sets available in the CDF-S survey region to
construct large but nearly uncontaminated samples of LBGs across a wide range
of redshift (0.5 < z < 4.5) which can be used as input samples for stacking
experiments. This approach allows us to trace the X-ray emission of Lyman Break
Galaxies to even lower, previously unreachable, flux density limits (~10^-18 mW
m^-2) and therefore to larger redshifts. We reliably detect soft-band X-ray
emission from all our input redshift bins except for the highest redshift (z~4)
one. From that we derive rest-frame 2-10 keV luminosities and infer star
formation rates and stellar masses. We find that star formation in LBGs peaks
at a redshift of z_peak~3.5 and then decreases quickly. We also see a
characteristic peak in the specific star formation rate (sSFR=SFR/M_*) at this
redshift. Furthermore, we calculate the contribution of LBGs to the total
cosmic star formation rate density (SFRD) and find that the contribution of
LBGs is negligible. Therefore, we conclude that most of the star formation in
the early universe takes place in lower luminosity galaxies as suggested by
hierarchical structure formation models.
Lyman Break Galaxies (LBGs) are widely thought to be prototypical young
galaxies in the early universe, particularly representative of those undergoing
massive events of star formation. Therefore, LBGs should produce significant
amounts of X-ray emission. We aim to trace the X-ray luminosity of Lyman Break
Galaxies across cosmic time and from that derive constraints on their star
formation history. We utilize the newly released 4 Ms mosaic obtained with the
Chandra X-ray Observatory, the deepest X-ray image to date, alongside with the
superb spectroscopic data sets available in the CDF-S survey region to
construct large but nearly uncontaminated samples of LBGs across a wide range
of redshift (0.5 < z < 4.5) which can be used as input samples for stacking
experiments. This approach allows us to trace the X-ray emission of Lyman Break
Galaxies to even lower, previously unreachable, flux density limits (~10^-18 mW
m^-2) and therefore to larger redshifts. We reliably detect soft-band X-ray
emission from all our input redshift bins except for the highest redshift (z~4)
one. From that we derive rest-frame 2-10 keV luminosities and infer star
formation rates and stellar masses. We find that star formation in LBGs peaks
at a redshift of z_peak~3.5 and then decreases quickly. We also see a
characteristic peak in the specific star formation rate (sSFR=SFR/M_*) at this
redshift. Furthermore, we calculate the contribution of LBGs to the total
cosmic star formation rate density (SFRD) and find that the contribution of
LBGs is negligible. Therefore, we conclude that most of the star formation in
the early universe takes place in lower luminosity galaxies as suggested by
hierarchical structure formation models.
Investigating the velocity structure and X-ray observable properties of simulated galaxy clusters with PHOX. (arXiv:1210.4158v1 [astro-ph.CO])
Investigating the velocity structure and X-ray observable properties of simulated galaxy clusters with PHOX. (arXiv:1210.4158v1 [astro-ph.CO]):
Non-thermal motions in the intra-cluster medium (ICM) are believed to play a
non-negligible role in the pressure support to the total gravitating mass of
galaxy clusters. Future X-ray missions, such as ASTRO-H and ATHENA, will
eventually allow us to directly detect the signature of these motions from
high-resolution spectra of the ICM. In this paper, we present a study on a set
of clusters extracted from a cosmological hydrodynamical simulation, devoted to
explore the role of non-thermal velocity amplitude in characterising the
cluster state and the relation between observed X-ray properties. In order to
reach this goal, we apply the X-ray virtual telescope PHOX to generate
synthetic observations of the simulated clusters with both Chandra and ATHENA,
the latter used as an example for the performance of very high-resolution X-ray
telescopes. From Chandra spectra we extract global properties, e.g. luminosity
and temperature, and from ATHENA spectra we estimate the gas velocity
dispersion along the line of sight from the broadening of heavy-ion emission
lines (e.g. Fe). We further extend the analysis to the relation between
non-thermal velocity dispersion of the gas and the L_X-T scaling law for the
simulated clusters. Interestingly, we find a clear dependence of slope and
scatter on the selection criterion for the clusters, based on the level of
significance of non-thermal motions. Namely, the scatter in the relation is
significantly reduced by the exclusion of the clusters, for which we estimate
the highest turbulent velocities. Such velocity diagnostics appears therefore
as a promising independent way to identify disturbed clusters, in addition to
the commonly used morphological inspection.
Non-thermal motions in the intra-cluster medium (ICM) are believed to play a
non-negligible role in the pressure support to the total gravitating mass of
galaxy clusters. Future X-ray missions, such as ASTRO-H and ATHENA, will
eventually allow us to directly detect the signature of these motions from
high-resolution spectra of the ICM. In this paper, we present a study on a set
of clusters extracted from a cosmological hydrodynamical simulation, devoted to
explore the role of non-thermal velocity amplitude in characterising the
cluster state and the relation between observed X-ray properties. In order to
reach this goal, we apply the X-ray virtual telescope PHOX to generate
synthetic observations of the simulated clusters with both Chandra and ATHENA,
the latter used as an example for the performance of very high-resolution X-ray
telescopes. From Chandra spectra we extract global properties, e.g. luminosity
and temperature, and from ATHENA spectra we estimate the gas velocity
dispersion along the line of sight from the broadening of heavy-ion emission
lines (e.g. Fe). We further extend the analysis to the relation between
non-thermal velocity dispersion of the gas and the L_X-T scaling law for the
simulated clusters. Interestingly, we find a clear dependence of slope and
scatter on the selection criterion for the clusters, based on the level of
significance of non-thermal motions. Namely, the scatter in the relation is
significantly reduced by the exclusion of the clusters, for which we estimate
the highest turbulent velocities. Such velocity diagnostics appears therefore
as a promising independent way to identify disturbed clusters, in addition to
the commonly used morphological inspection.
Suzaku observations of 'bare' active galactic nuclei. (arXiv:1210.4593v1 [astro-ph.HE])
Suzaku observations of 'bare' active galactic nuclei. (arXiv:1210.4593v1 [astro-ph.HE]):
We present a X-ray spectral analysis of a large sample of 25 'bare' active
galactic nuclei, sources with little or no complicating intrinsic absorption,
observed with Suzaku. Our work focuses on studying the potential contribution
from relativistic disc reflection, and examining the implications of this
interpretation for the intrinsic spectral complexities frequently displayed by
AGN in the X-ray bandpass. During the analysis, we take the unique approach of
attempting to simultaneously undertake a systematic analysis of the whole
sample, as well as a detailed treatment of each individual source, and find
that disc reflection has the required flexibility to successfully reproduce the
broadband spectrum observed for all of the sources considered. Where possible,
we use the reflected emission to place constraints on the black hole spin for
this sample of sources. Our analysis suggests a general preference for rapidly
rotating black holes, which if taken at face value is most consistent with the
scenario in which SMBH growth is dominated by prolonged, ordered accretion.
However, there may be observational biases towards AGN with high spin in the
compiled sample, limiting our ability to draw strong conclusions for the
general population at this stage. Finally, contrary to popular belief, our
analysis also implies that the dichotomy between radio loud/radio quiet AGN is
not solely related to black hole spin.
We present a X-ray spectral analysis of a large sample of 25 'bare' active
galactic nuclei, sources with little or no complicating intrinsic absorption,
observed with Suzaku. Our work focuses on studying the potential contribution
from relativistic disc reflection, and examining the implications of this
interpretation for the intrinsic spectral complexities frequently displayed by
AGN in the X-ray bandpass. During the analysis, we take the unique approach of
attempting to simultaneously undertake a systematic analysis of the whole
sample, as well as a detailed treatment of each individual source, and find
that disc reflection has the required flexibility to successfully reproduce the
broadband spectrum observed for all of the sources considered. Where possible,
we use the reflected emission to place constraints on the black hole spin for
this sample of sources. Our analysis suggests a general preference for rapidly
rotating black holes, which if taken at face value is most consistent with the
scenario in which SMBH growth is dominated by prolonged, ordered accretion.
However, there may be observational biases towards AGN with high spin in the
compiled sample, limiting our ability to draw strong conclusions for the
general population at this stage. Finally, contrary to popular belief, our
analysis also implies that the dichotomy between radio loud/radio quiet AGN is
not solely related to black hole spin.
Black hole masses from X-rays. (arXiv:1210.4558v1 [astro-ph.HE])
Black hole masses from X-rays. (arXiv:1210.4558v1 [astro-ph.HE]):
We discuss two methods to estimate black hole (BH) masses using X-ray data
only: from the X-ray variability amplitude and from the photon index Gamma. The
first method is based on the anti-correlation between BH mass and X-ray
variability amplitude. Using a sample of AGN with BH masses from reverberation
mapping, we show that this method shows small intrinsic scatter. The second
method is based on the correlation between Gamma and both the Eddington ratio
L_{bol}/L_{Edd} and the bolometric correction L_{bol}/L_{2-10keV}.
We discuss two methods to estimate black hole (BH) masses using X-ray data
only: from the X-ray variability amplitude and from the photon index Gamma. The
first method is based on the anti-correlation between BH mass and X-ray
variability amplitude. Using a sample of AGN with BH masses from reverberation
mapping, we show that this method shows small intrinsic scatter. The second
method is based on the correlation between Gamma and both the Eddington ratio
L_{bol}/L_{Edd} and the bolometric correction L_{bol}/L_{2-10keV}.
Monday, October 15, 2012
Nonthermal X-rays from low-energy cosmic rays: Application to the 6.4 keV line emission from the Arches cluster region. (arXiv:1210.2108v1 [astro-ph.HE])
Nonthermal X-rays from low-energy cosmic rays: Application to the 6.4 keV line emission from the Arches cluster region. (arXiv:1210.2108v1 [astro-ph.HE]):
The iron line at 6.4 keV provides a valuable spectral diagnostic in several
fields of X-ray astronomy. It often results from the reprocessing of external
X-rays by a neutral or low-ionized medium, but it can also be excited by
impacts of low-energy cosmic rays. This paper aims to provide signatures
allowing identification of radiation from low-energy cosmic rays in X-ray
spectra showing the 6.4 keV line. We study in detail the production of
nonthermal line and continuum X-rays by interaction of accelerated electrons
and ions with a neutral ambient gas. Corresponding models are then applied to
XMM-Newton observations of the X-ray emission emanating from the Arches cluster
region near the Galactic center. Bright 6.4 keV line structures are observed
around the Arches cluster. This emission is very likely produced by cosmic
rays. We find that it can result from the bombardment of molecular gas by
energetic ions, but probably not by accelerated electrons. Using a model of
X-ray production by cosmic-ray ions, we obtain a best-fit metallicity of the
ambient medium of 1.7 plus-minus 0.2 times the solar metallicity. A large flux
of low-energy cosmic ray ions could be produced in the ongoing supersonic
collision between the star cluster and an adjacent molecular cloud. We find
that a particle acceleration efficiency in the resulting shock system of a few
percent would give enough power in the cosmic rays to explain the luminosity of
the nonthermal X-ray emission. Depending on the unknown shape of the kinetic
energy distribution of the fast ions above 1 GeV per nucleon, the Arches
cluster region may be a source of high-energy gamma-rays detectable with the
Fermi Gamma-ray Space Telescope. At present, the X-ray emission prominent in
the 6.4 keV Fe line emanating from the Arches cluster region probably offers
the best available signature for a source of low-energy hadronic cosmic rays in
the Galaxy.
The iron line at 6.4 keV provides a valuable spectral diagnostic in several
fields of X-ray astronomy. It often results from the reprocessing of external
X-rays by a neutral or low-ionized medium, but it can also be excited by
impacts of low-energy cosmic rays. This paper aims to provide signatures
allowing identification of radiation from low-energy cosmic rays in X-ray
spectra showing the 6.4 keV line. We study in detail the production of
nonthermal line and continuum X-rays by interaction of accelerated electrons
and ions with a neutral ambient gas. Corresponding models are then applied to
XMM-Newton observations of the X-ray emission emanating from the Arches cluster
region near the Galactic center. Bright 6.4 keV line structures are observed
around the Arches cluster. This emission is very likely produced by cosmic
rays. We find that it can result from the bombardment of molecular gas by
energetic ions, but probably not by accelerated electrons. Using a model of
X-ray production by cosmic-ray ions, we obtain a best-fit metallicity of the
ambient medium of 1.7 plus-minus 0.2 times the solar metallicity. A large flux
of low-energy cosmic ray ions could be produced in the ongoing supersonic
collision between the star cluster and an adjacent molecular cloud. We find
that a particle acceleration efficiency in the resulting shock system of a few
percent would give enough power in the cosmic rays to explain the luminosity of
the nonthermal X-ray emission. Depending on the unknown shape of the kinetic
energy distribution of the fast ions above 1 GeV per nucleon, the Arches
cluster region may be a source of high-energy gamma-rays detectable with the
Fermi Gamma-ray Space Telescope. At present, the X-ray emission prominent in
the 6.4 keV Fe line emanating from the Arches cluster region probably offers
the best available signature for a source of low-energy hadronic cosmic rays in
the Galaxy.
A general relativistic model of accretion disks with coronae surrounding Kerr black holes. (arXiv:1210.2662v1 [astro-ph.HE])
A general relativistic model of accretion disks with coronae surrounding Kerr black holes. (arXiv:1210.2662v1 [astro-ph.HE]):
We calculate the structure of a standard accretion disk with corona
surrounding a massive Kerr black hole in general relativistic frame, in which
the corona is assumed to be heated by the reconnection of the strongly buoyant
magnetic fields generated in the cold accretion disk. The emergent spectra of
the accretion disk-corona systems are calculated by using the relativistic
ray-tracing method. We propose a new method to calculate the emergent
Comptonized spectra from the coronae. The spectra of the disk-corona systems
with a modified $\alpha$-magnetic stress show that both the hard X-ray spectral
index and the hard X-ray bolometric correction factor $L_{\rm bol}/L_{\rm
X,2-10keV}$ increase with the dimensionless mass accretion rate, which are
qualitatively consistent with the observations of active galactic nuclei
(AGNs). The fraction of the power dissipated in the corona decreases with
increasing black hole spin parameter $a$, which leads to lower electron
temperatures of the coronas for rapidly spinning black holes. The X-ray
emission from the coronas surrounding rapidly spinning black holes becomes weak
and soft. The ratio of the X-ray luminosity to the optical/UV luminosity
increases with the viewing angle, while the spectral shape in the X-ray band is
insensitive with the viewing angle. We find that the spectral index in the
infrared waveband depends on the mass accretion rate and the black hole spin
$a$, which deviates from $f_\nu\propto\nu^{1/3}$ expected by the standard thin
disk model.
We calculate the structure of a standard accretion disk with corona
surrounding a massive Kerr black hole in general relativistic frame, in which
the corona is assumed to be heated by the reconnection of the strongly buoyant
magnetic fields generated in the cold accretion disk. The emergent spectra of
the accretion disk-corona systems are calculated by using the relativistic
ray-tracing method. We propose a new method to calculate the emergent
Comptonized spectra from the coronae. The spectra of the disk-corona systems
with a modified $\alpha$-magnetic stress show that both the hard X-ray spectral
index and the hard X-ray bolometric correction factor $L_{\rm bol}/L_{\rm
X,2-10keV}$ increase with the dimensionless mass accretion rate, which are
qualitatively consistent with the observations of active galactic nuclei
(AGNs). The fraction of the power dissipated in the corona decreases with
increasing black hole spin parameter $a$, which leads to lower electron
temperatures of the coronas for rapidly spinning black holes. The X-ray
emission from the coronas surrounding rapidly spinning black holes becomes weak
and soft. The ratio of the X-ray luminosity to the optical/UV luminosity
increases with the viewing angle, while the spectral shape in the X-ray band is
insensitive with the viewing angle. We find that the spectral index in the
infrared waveband depends on the mass accretion rate and the black hole spin
$a$, which deviates from $f_\nu\propto\nu^{1/3}$ expected by the standard thin
disk model.
Galactic Winds in Cosmological Simulations of the Circumgalactic Medium. (arXiv:1210.3582v1 [astro-ph.CO])
Galactic Winds in Cosmological Simulations of the Circumgalactic Medium. (arXiv:1210.3582v1 [astro-ph.CO]):
(Abridged) We explore new observationally-constrained sub-resolution models
of galactic outflows and investigate their impact on the circumgalactic medium
(CGM) over redshifts z = 2 - 4. We perform cosmological hydrodynamic
simulations, including star formation, chemical enrichment, and four cases of
SNe-driven outflows: no wind (NW), an energy-driven constant velocity wind
(CW), a radially varying wind (RVWa) where the outflow velocity has a positive
correlation with galactocentric distance (r), and a RVW with additional
dependence on halo mass (RVWb). Overall, we find that the outflows expel
metal-enriched gas away from galaxies, significantly quench star formation, and
enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy
centers are most sensitive to the choice of the wind model for halo masses
(10^9 - 10^11) M_sun. We infer that the RVWb model is similar to the NW case,
except that it substantially enriches the CGM: the carbon metallicity (Z_C) is
10 times higher in RVWb than in NW at r > R_200; and the warm gas of 10^4 -
10^5 K and delta < 100 is enriched to 50 times higher than in NW. We also find
that the impact of models CW and RVWa are similar, with the following
differences. RVWa causes a greater suppression of star formation rate at z < 5,
and has a higher fraction of low-density (delta < 10), warm-hot (10^4 - 10^6 K)
gas than in CW. Outflows in CW produce a higher and earlier enrichment of some
IGM phases than RVWa. By visual inspection, we note that the RVWa model shows
more pronounced bipolar outflows and galactic disks. We present fitting
formulae for [Z_C-delta] and [Z_C-r], also for the abundance of CIV as a
function of r. We predict observational diagnostics to distinguish between
different outflow scenarios: Z_C of the CGM gas at r = (30 - 300) kpc/h
comoving, and CIV fraction of the inner gas at r < (4 - 5) kpc/h comoving.
(Abridged) We explore new observationally-constrained sub-resolution models
of galactic outflows and investigate their impact on the circumgalactic medium
(CGM) over redshifts z = 2 - 4. We perform cosmological hydrodynamic
simulations, including star formation, chemical enrichment, and four cases of
SNe-driven outflows: no wind (NW), an energy-driven constant velocity wind
(CW), a radially varying wind (RVWa) where the outflow velocity has a positive
correlation with galactocentric distance (r), and a RVW with additional
dependence on halo mass (RVWb). Overall, we find that the outflows expel
metal-enriched gas away from galaxies, significantly quench star formation, and
enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy
centers are most sensitive to the choice of the wind model for halo masses
(10^9 - 10^11) M_sun. We infer that the RVWb model is similar to the NW case,
except that it substantially enriches the CGM: the carbon metallicity (Z_C) is
10 times higher in RVWb than in NW at r > R_200; and the warm gas of 10^4 -
10^5 K and delta < 100 is enriched to 50 times higher than in NW. We also find
that the impact of models CW and RVWa are similar, with the following
differences. RVWa causes a greater suppression of star formation rate at z < 5,
and has a higher fraction of low-density (delta < 10), warm-hot (10^4 - 10^6 K)
gas than in CW. Outflows in CW produce a higher and earlier enrichment of some
IGM phases than RVWa. By visual inspection, we note that the RVWa model shows
more pronounced bipolar outflows and galactic disks. We present fitting
formulae for [Z_C-delta] and [Z_C-r], also for the abundance of CIV as a
function of r. We predict observational diagnostics to distinguish between
different outflow scenarios: Z_C of the CGM gas at r = (30 - 300) kpc/h
comoving, and CIV fraction of the inner gas at r < (4 - 5) kpc/h comoving.
Thermal and non-thermal traces of AGN feedback: results from cosmological AMR simulations. (arXiv:1210.3541v1 [astro-ph.CO])
Thermal and non-thermal traces of AGN feedback: results from cosmological AMR simulations. (arXiv:1210.3541v1 [astro-ph.CO]):
We investigate the observable effects of feedback from Active Galactic Nuclei
(AGN) on non-thermal components of the intracluster medium (ICM). We have
modelled feedback from AGN in cosmological simulations with the adaptive mesh
refinement code ENZO, investigating three types of feedback that are sometimes
called quasar, jet and radio mode. Using a small set of galaxy clusters
simulated at high resolution, we model the injection and evolution of Cosmic
Rays, as well as their effects on the thermal plasma. By comparing, both, the
profiles of thermal gas to observed profiles from the ACCEPT sample, and the
secondary gamma-ray emission to the available upper limits from FERMI, we
discuss how the combined analysis of these two observables can constrain the
energetics and mechanisms of feedback models in clusters. Those modes of AGN
feedback that provide a good match to X-ray observations, yield a gamma-ray
luminosity resulting from secondary cosmic rays that is about below the
available upper limits from FERMI. Moreover, we investigate the injection of
turbulent motions into the ICM from AGN, and the detectability of these motions
via the analysis of line broadening of the Fe XXIII line. In the near future,
deeper observations/upper-limits of non-thermal emissions from galaxy clusters
will yield stringent constraints on the energetics and modes of AGN feedback,
even at early cosmic epochs.
We investigate the observable effects of feedback from Active Galactic Nuclei
(AGN) on non-thermal components of the intracluster medium (ICM). We have
modelled feedback from AGN in cosmological simulations with the adaptive mesh
refinement code ENZO, investigating three types of feedback that are sometimes
called quasar, jet and radio mode. Using a small set of galaxy clusters
simulated at high resolution, we model the injection and evolution of Cosmic
Rays, as well as their effects on the thermal plasma. By comparing, both, the
profiles of thermal gas to observed profiles from the ACCEPT sample, and the
secondary gamma-ray emission to the available upper limits from FERMI, we
discuss how the combined analysis of these two observables can constrain the
energetics and mechanisms of feedback models in clusters. Those modes of AGN
feedback that provide a good match to X-ray observations, yield a gamma-ray
luminosity resulting from secondary cosmic rays that is about below the
available upper limits from FERMI. Moreover, we investigate the injection of
turbulent motions into the ICM from AGN, and the detectability of these motions
via the analysis of line broadening of the Fe XXIII line. In the near future,
deeper observations/upper-limits of non-thermal emissions from galaxy clusters
will yield stringent constraints on the energetics and modes of AGN feedback,
even at early cosmic epochs.
The X-ray Star Formation Story as Told by Lyman Break Galaxies in the 4 Ms CDF-S. (arXiv:1210.3357v1 [astro-ph.CO])
The X-ray Star Formation Story as Told by Lyman Break Galaxies in the 4 Ms CDF-S. (arXiv:1210.3357v1 [astro-ph.CO]):
We present results from deep X-ray stacking of >4000 high redshift galaxies
from z~1 to 8 using the 4 Ms Chandra Deep Field South (CDF-S) data, the deepest
X-ray survey of the extragalactic sky to date. The galaxy samples were selected
using the Lyman break technique based primarily on recent HST ACS and WFC3
observations. Based on such high specific star formation rates (sSFRs): log
SFR/M* > -8.7, we expect that the observed properties of these LBGs are
dominated by young stellar populations. The X-ray emission in LBGs, eliminating
individually detected X-ray sources (potential AGN), is expected to be powered
by X-ray binaries and hot gas. We find, for the first time, evidence of
evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z<4
LBGs (covering ~90% of the Universe's history), we find that the 2-10 keV X-ray
luminosity evolves weakly with redshift (z) and SFR as log LX = 0.93 log (1+z)
+ 0.65 log SFR + 39.80. By comparing our observations with sophisticated X-ray
binary population synthesis models, we interpret that the redshift evolution of
LX/SFR is driven by metallicity evolution in HMXBs, likely the dominant
population in these high sSFR galaxies. We also compare these models with our
observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc^3)
and find excellent agreement. While there are no significant stacked detections
at z>5, we use our upper limits from 5<z<8 LBGs to constrain the SMBH accretion
history of the Universe around the epoch of reionization.
We present results from deep X-ray stacking of >4000 high redshift galaxies
from z~1 to 8 using the 4 Ms Chandra Deep Field South (CDF-S) data, the deepest
X-ray survey of the extragalactic sky to date. The galaxy samples were selected
using the Lyman break technique based primarily on recent HST ACS and WFC3
observations. Based on such high specific star formation rates (sSFRs): log
SFR/M* > -8.7, we expect that the observed properties of these LBGs are
dominated by young stellar populations. The X-ray emission in LBGs, eliminating
individually detected X-ray sources (potential AGN), is expected to be powered
by X-ray binaries and hot gas. We find, for the first time, evidence of
evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z<4
LBGs (covering ~90% of the Universe's history), we find that the 2-10 keV X-ray
luminosity evolves weakly with redshift (z) and SFR as log LX = 0.93 log (1+z)
+ 0.65 log SFR + 39.80. By comparing our observations with sophisticated X-ray
binary population synthesis models, we interpret that the redshift evolution of
LX/SFR is driven by metallicity evolution in HMXBs, likely the dominant
population in these high sSFR galaxies. We also compare these models with our
observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc^3)
and find excellent agreement. While there are no significant stacked detections
at z>5, we use our upper limits from 5<z<8 LBGs to constrain the SMBH accretion
history of the Universe around the epoch of reionization.
Friday, October 12, 2012
Constraints on Compton-thick winds from black hole accretion disks: can we see the inner disk?. (arXiv:1210.3029v1 [astro-ph.HE])
Constraints on Compton-thick winds from black hole accretion disks: can we see the inner disk?. (arXiv:1210.3029v1 [astro-ph.HE]):
Strong evidence is emerging that winds can be driven from the central regions
of accretion disks in both active galactic nuclei (AGN) and Galactic black hole
binaries (GBHBs). Direct evidence for highly-ionized, Compton-thin inner-disk
winds comes from observations of blueshifted (v~0.05-0.1c) iron-K X-ray
absorption lines. However, it has been suggested that the inner regions of
black hole accretion disks can also drive Compton-thick winds --- such winds
would enshroud the inner disk, preventing us from seeing direct signatures of
the accretion disk (i.e. the photospheric thermal emission, or the
Doppler/gravitationally broadened iron K-alpha line). Here, we show that,
provided the source is sub-Eddington, the well-established wind driving
mechanisms fail to launch a Compton-thick wind from the inner disk. For the
accelerated region of the wind to be Compton-thick, the momentum carried in the
wind must exceed the available photon momentum by a factor of at least
2/lambda, where lambda is the Eddington ratio of the source, ruling out
radiative acceleration unless the source is very close to the Eddington limit.
Compton-thick winds also carry large mass-fluxes, and a consideration of the
connections between the wind and the disk show this to be incompatible with
magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out
on the basis of the large Compton-radii that typify black hole systems. In the
absence of some new acceleration mechanism, we conclude that the inner regions
of sub-Eddington accretion disks around black holes are indeed naked.
Strong evidence is emerging that winds can be driven from the central regions
of accretion disks in both active galactic nuclei (AGN) and Galactic black hole
binaries (GBHBs). Direct evidence for highly-ionized, Compton-thin inner-disk
winds comes from observations of blueshifted (v~0.05-0.1c) iron-K X-ray
absorption lines. However, it has been suggested that the inner regions of
black hole accretion disks can also drive Compton-thick winds --- such winds
would enshroud the inner disk, preventing us from seeing direct signatures of
the accretion disk (i.e. the photospheric thermal emission, or the
Doppler/gravitationally broadened iron K-alpha line). Here, we show that,
provided the source is sub-Eddington, the well-established wind driving
mechanisms fail to launch a Compton-thick wind from the inner disk. For the
accelerated region of the wind to be Compton-thick, the momentum carried in the
wind must exceed the available photon momentum by a factor of at least
2/lambda, where lambda is the Eddington ratio of the source, ruling out
radiative acceleration unless the source is very close to the Eddington limit.
Compton-thick winds also carry large mass-fluxes, and a consideration of the
connections between the wind and the disk show this to be incompatible with
magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out
on the basis of the large Compton-radii that typify black hole systems. In the
absence of some new acceleration mechanism, we conclude that the inner regions
of sub-Eddington accretion disks around black holes are indeed naked.
Tuesday, October 9, 2012
Equation of state of magnetar crusts from Hartree-Fock-Bogoliubov atomic mass models. (arXiv:1210.1668v1 [astro-ph.HE])
Equation of state of magnetar crusts from Hartree-Fock-Bogoliubov atomic mass models. (arXiv:1210.1668v1 [astro-ph.HE]):
The equation of state (EoS) of the outer crust of a cold non-accreting
magnetar has been determined using the model of Lai and Shapiro (1991). For
this purpose, we have made use of the latest experimental atomic mass data
complemented with a Hartree-Fock-Bogoliubov (HFB) mass model. Magnetar crusts
are found to be significantly different from the crusts of ordinary neutron
stars.
The equation of state (EoS) of the outer crust of a cold non-accreting
magnetar has been determined using the model of Lai and Shapiro (1991). For
this purpose, we have made use of the latest experimental atomic mass data
complemented with a Hartree-Fock-Bogoliubov (HFB) mass model. Magnetar crusts
are found to be significantly different from the crusts of ordinary neutron
stars.
No surviving evolved companions to the progenitor of supernova SN 1006. (arXiv:1210.1948v1 [astro-ph.GA])
No surviving evolved companions to the progenitor of supernova SN 1006. (arXiv:1210.1948v1 [astro-ph.GA]):
Type Ia supernovae are thought to occur as a white dwarf made of carbon and
oxygen accretes sufficient mass to trigger a thermonuclear explosion$^{1}$. The
accretion could occur slowly from an unevolved (main-sequence) or evolved
(subgiant or giant) star$^{2,3}$, that being dubbed the single-degenerate
channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double-
degenerate channel)$^{3,4}$. Obviously, a companion will survive the explosion
only in the single-degenerate channel$^{5}$. Both channels might contribute to
the production of type Ia supernovae$^{6,7}$ but their relative proportions
still remain a fundamental puzzle in astronomy. Previous searches for remnant
companions have revealed one possible case for SN 1572$^{8,9}$, though that has
been criticized$^{10}$. More recently, observations have restricted surviving
companions to be small, main-sequence stars$^{11,12,13}$, ruling out giant
companions, though still allowing the single-degenerate channel. Here we report
the result of a search for surviving companions to the progenitor of SN
1006$^{14}$. None of the stars within 4' of the apparent site of the explosion
is associated with the supernova remnant, so we can firmly exclude all giant
and subgiant companions to the progenitor. Combined with the previous results,
less than 20 per cent of type Iae occur through the single degenerate channel.
Type Ia supernovae are thought to occur as a white dwarf made of carbon and
oxygen accretes sufficient mass to trigger a thermonuclear explosion$^{1}$. The
accretion could occur slowly from an unevolved (main-sequence) or evolved
(subgiant or giant) star$^{2,3}$, that being dubbed the single-degenerate
channel, or rapidly as it breaks up a smaller orbiting white dwarf (the double-
degenerate channel)$^{3,4}$. Obviously, a companion will survive the explosion
only in the single-degenerate channel$^{5}$. Both channels might contribute to
the production of type Ia supernovae$^{6,7}$ but their relative proportions
still remain a fundamental puzzle in astronomy. Previous searches for remnant
companions have revealed one possible case for SN 1572$^{8,9}$, though that has
been criticized$^{10}$. More recently, observations have restricted surviving
companions to be small, main-sequence stars$^{11,12,13}$, ruling out giant
companions, though still allowing the single-degenerate channel. Here we report
the result of a search for surviving companions to the progenitor of SN
1006$^{14}$. None of the stars within 4' of the apparent site of the explosion
is associated with the supernova remnant, so we can firmly exclude all giant
and subgiant companions to the progenitor. Combined with the previous results,
less than 20 per cent of type Iae occur through the single degenerate channel.
Structure of Quark Stars. (arXiv:1210.1910v1 [astro-ph.SR])
Structure of Quark Stars. (arXiv:1210.1910v1 [astro-ph.SR]):
This paper gives an brief overview of the structure of hypothetical strange
quarks stars (quark stars, for short), which are made of absolutely stable
3-flavor strange quark matter. Such objects can be either bare or enveloped in
thin nuclear crusts, which consist of heavy ions immersed in an electron gas.
In contrast to neutron stars, the structure of quark stars is determined by two
(rather than one) parameters, the central star density and the density at the
base of the crust. If bare, quark stars possess ultra-high electric fields on
the order of 10^{18} to 10^{19} V/cm. These features render the properties of
quark stars more multifaceted than those of neutron stars and may allow one to
observationally distinguish quark stars from neutron stars.
This paper gives an brief overview of the structure of hypothetical strange
quarks stars (quark stars, for short), which are made of absolutely stable
3-flavor strange quark matter. Such objects can be either bare or enveloped in
thin nuclear crusts, which consist of heavy ions immersed in an electron gas.
In contrast to neutron stars, the structure of quark stars is determined by two
(rather than one) parameters, the central star density and the density at the
base of the crust. If bare, quark stars possess ultra-high electric fields on
the order of 10^{18} to 10^{19} V/cm. These features render the properties of
quark stars more multifaceted than those of neutron stars and may allow one to
observationally distinguish quark stars from neutron stars.
Friday, October 5, 2012
Galactic Outflows in Absorption and Emission: Near-UV Spectroscopy of Galaxies at 1 < z < 2. (arXiv:1209.4903v1 [astro-ph.CO])
Galactic Outflows in Absorption and Emission: Near-UV Spectroscopy of Galaxies at 1<z<2. (arXiv:1209.4903v1 [astro-ph.CO]):
We study large-scale outflows in a sample of 96 star-forming galaxies at
1<z<2, using near-UV spectroscopy of FeII and MgII absorption and emission. The
average blueshift of the FeII interstellar absorption lines with respect to the
systemic velocity is -85+/-10 km/s at z~1.5, with standard deviation 87 km/s;
this is a decrease of a factor of two from the average blueshift measured for
far-UV interstellar absorption lines in similarly selected galaxies at z~2. The
profiles of the MgII 2796, 2803 lines show much more variety than the FeII
profiles, which are always seen in absorption; MgII ranges from strong emission
to pure absorption, with emission more common in galaxies with blue UV slopes
and at lower stellar masses. Outflow velocities, as traced by the centroids and
maximum extent of the absorption lines, increase with increasing stellar mass
with 2-3sigma significance, in agreement with previous results. We study fine
structure emission from FeII*, finding several lines of evidence in support of
the model in which this emission is generated by the re-emission of continuum
photons absorbed in the FeII resonance transitions in outflowing gas. In
contrast, photoionization models indicate that MgII emission arises from the
resonant scattering of photons produced in HII regions, accounting for the
differing profiles of the MgII and FeII lines. A comparison of the strengths of
the FeII absorption and FeII* emission lines indicates that massive galaxies
have more extended outflows and/or greater extinction, while two-dimensional
composite spectra indicate that emission from the outflow is stronger at a
radius of ~10 kpc in high mass galaxies than in low mass galaxies.
We study large-scale outflows in a sample of 96 star-forming galaxies at
1<z<2, using near-UV spectroscopy of FeII and MgII absorption and emission. The
average blueshift of the FeII interstellar absorption lines with respect to the
systemic velocity is -85+/-10 km/s at z~1.5, with standard deviation 87 km/s;
this is a decrease of a factor of two from the average blueshift measured for
far-UV interstellar absorption lines in similarly selected galaxies at z~2. The
profiles of the MgII 2796, 2803 lines show much more variety than the FeII
profiles, which are always seen in absorption; MgII ranges from strong emission
to pure absorption, with emission more common in galaxies with blue UV slopes
and at lower stellar masses. Outflow velocities, as traced by the centroids and
maximum extent of the absorption lines, increase with increasing stellar mass
with 2-3sigma significance, in agreement with previous results. We study fine
structure emission from FeII*, finding several lines of evidence in support of
the model in which this emission is generated by the re-emission of continuum
photons absorbed in the FeII resonance transitions in outflowing gas. In
contrast, photoionization models indicate that MgII emission arises from the
resonant scattering of photons produced in HII regions, accounting for the
differing profiles of the MgII and FeII lines. A comparison of the strengths of
the FeII absorption and FeII* emission lines indicates that massive galaxies
have more extended outflows and/or greater extinction, while two-dimensional
composite spectra indicate that emission from the outflow is stronger at a
radius of ~10 kpc in high mass galaxies than in low mass galaxies.
Measuring the Mass Distribution in Galaxy Clusters. (arXiv:1209.5675v1 [astro-ph.CO])
Measuring the Mass Distribution in Galaxy Clusters. (arXiv:1209.5675v1 [astro-ph.CO]):
Cluster mass profiles are tests of models of structure formation. Only two
current observational methods of determining the mass profile, gravitational
lensing and the caustic technique, are independent of the assumption of
dynamical equilibrium. Both techniques enable determination of the extended
mass profile at radii beyond the virial radius. For 19 clusters, we compare the
mass profile based on the caustic technique with weak lensing measurements
taken from the literature. This comparison offers a test of systematic issues
in both techniques. Around the virial radius, the two methods of mass
estimation agree to within about 30%, consistent with the expected errors in
the individual techniques. At small radii, the caustic technique overestimates
the mass as expected from numerical simulations. The ratio between the lensing
profile and the caustic mass profile at these radii suggests that the weak
lensing profiles are a good representation of the true mass profile. At radii
larger than the virial radius, the lensing mass profile exceeds the caustic
mass profile possibly as a result of contamination of the lensing profile by
large-scale structures within the lensing kernel. We highlight the case of the
closely neighboring clusters MS0906+11 and A750 to illustrate the potential
seriousness of contamination of the the weak lensing signal by unrelated
structures.
Cluster mass profiles are tests of models of structure formation. Only two
current observational methods of determining the mass profile, gravitational
lensing and the caustic technique, are independent of the assumption of
dynamical equilibrium. Both techniques enable determination of the extended
mass profile at radii beyond the virial radius. For 19 clusters, we compare the
mass profile based on the caustic technique with weak lensing measurements
taken from the literature. This comparison offers a test of systematic issues
in both techniques. Around the virial radius, the two methods of mass
estimation agree to within about 30%, consistent with the expected errors in
the individual techniques. At small radii, the caustic technique overestimates
the mass as expected from numerical simulations. The ratio between the lensing
profile and the caustic mass profile at these radii suggests that the weak
lensing profiles are a good representation of the true mass profile. At radii
larger than the virial radius, the lensing mass profile exceeds the caustic
mass profile possibly as a result of contamination of the lensing profile by
large-scale structures within the lensing kernel. We highlight the case of the
closely neighboring clusters MS0906+11 and A750 to illustrate the potential
seriousness of contamination of the the weak lensing signal by unrelated
structures.
High-Resolution X-Ray Spectroscopy of the Galactic Supernova Remnant Puppis A with the XMM-Newton RGS. (arXiv:1209.5496v2 [astro-ph.HE] UPDATED)
High-Resolution X-Ray Spectroscopy of the Galactic Supernova Remnant Puppis A with the XMM-Newton RGS. (arXiv:1209.5496v2 [astro-ph.HE] UPDATED):
We present high-resolution X-ray spectra of cloud-shock interaction regions
in the eastern and northern rims of the Galactic supernova remnant Puppis A,
using the Reflection Grating Spectrometer onboard the XMM-Newton satellite. A
number of emission lines including K alpha triplets of He-like N, O, and Ne are
clearly resolved for the first time. Intensity ratios of forbidden to resonance
lines in the triplets are found to be higher than predictions by thermal
emission models having plausible plasma parameters. The anomalous line ratios
cannot be reproduced by effects of resonance scattering, recombination, or
inner-shell ionization processes, but could be explained by charge-exchange
emission that should arise at interfaces between the cold/warm clouds and the
hot plasma. Our observations thus provide observational support for
charge-exchange X-ray emission in supernova remnants.
We present high-resolution X-ray spectra of cloud-shock interaction regions
in the eastern and northern rims of the Galactic supernova remnant Puppis A,
using the Reflection Grating Spectrometer onboard the XMM-Newton satellite. A
number of emission lines including K alpha triplets of He-like N, O, and Ne are
clearly resolved for the first time. Intensity ratios of forbidden to resonance
lines in the triplets are found to be higher than predictions by thermal
emission models having plausible plasma parameters. The anomalous line ratios
cannot be reproduced by effects of resonance scattering, recombination, or
inner-shell ionization processes, but could be explained by charge-exchange
emission that should arise at interfaces between the cold/warm clouds and the
hot plasma. Our observations thus provide observational support for
charge-exchange X-ray emission in supernova remnants.
Constraining the fraction of Compton-thick AGN in the Universe by modelling the diffuse X-ray background spectrum. (arXiv:1209.5398v1 [astro-ph.HE])
Constraining the fraction of Compton-thick AGN in the Universe by modelling the diffuse X-ray background spectrum. (arXiv:1209.5398v1 [astro-ph.HE]):
This paper investigates what constraints can be placed on the fraction of
Compton-thick (CT) AGN in the Universe from the modeling of the spectrum of the
diffuse X-ray background (XRB). We present a model for the synthesis of the XRB
that uses as input a library of AGN X-ray spectra generated by the Monte Carlo
simulations described by Brightman & Nandra. This is essential to account for
the Compton scattering of X-ray photons in a dense medium and the impact of
that process on the spectra of obscured AGN. We identify a small number of
input parameters to the XRB synthesis code which encapsulate the minimum level
of uncertainty in reconstructing the XRB spectrum. These are the power-law
index and high energy cutoff of the intrinsic X-ray spectra of AGN, the level
of the reflection component in AGN spectra and the fraction of CT AGN in the
Universe. We then map the volume of the space allowed to these parameters by
current observations of the XRB spectrum in the range 3-100 keV. One of the
least constrained parameters is the fraction of CT AGN. Statistically
acceptable fits to the XRB spectrum at the 68% confidence level can be obtained
for CT fractions in the range 5-50%. This is because of degeneracies among
input parameters to the XRB synthesis code and uncertainties in the modeling of
AGN spectra (e.g. reflection). The most promising route for constraining the
fraction of CT AGN in the Universe is via the direct detection of those sources
in high energy (>10keV) surveys. It is shown that the observed fraction of CT
sources identified in the SWIFT/BAT survey, limits the intrinsic fraction of CT
AGN, at least at low redshift, to 10-20% (68% confidence level). We also make
predictions on the number density of CT sources that current and future X-ray
missions are expected to discover. Testing those predictions will constrain the
intrinsic fraction of CT AGN as a function of redshift.
This paper investigates what constraints can be placed on the fraction of
Compton-thick (CT) AGN in the Universe from the modeling of the spectrum of the
diffuse X-ray background (XRB). We present a model for the synthesis of the XRB
that uses as input a library of AGN X-ray spectra generated by the Monte Carlo
simulations described by Brightman & Nandra. This is essential to account for
the Compton scattering of X-ray photons in a dense medium and the impact of
that process on the spectra of obscured AGN. We identify a small number of
input parameters to the XRB synthesis code which encapsulate the minimum level
of uncertainty in reconstructing the XRB spectrum. These are the power-law
index and high energy cutoff of the intrinsic X-ray spectra of AGN, the level
of the reflection component in AGN spectra and the fraction of CT AGN in the
Universe. We then map the volume of the space allowed to these parameters by
current observations of the XRB spectrum in the range 3-100 keV. One of the
least constrained parameters is the fraction of CT AGN. Statistically
acceptable fits to the XRB spectrum at the 68% confidence level can be obtained
for CT fractions in the range 5-50%. This is because of degeneracies among
input parameters to the XRB synthesis code and uncertainties in the modeling of
AGN spectra (e.g. reflection). The most promising route for constraining the
fraction of CT AGN in the Universe is via the direct detection of those sources
in high energy (>10keV) surveys. It is shown that the observed fraction of CT
sources identified in the SWIFT/BAT survey, limits the intrinsic fraction of CT
AGN, at least at low redshift, to 10-20% (68% confidence level). We also make
predictions on the number density of CT sources that current and future X-ray
missions are expected to discover. Testing those predictions will constrain the
intrinsic fraction of CT AGN as a function of redshift.
Isotropic Heating of Galaxy Cluster Cores via Rapidly Reorienting AGN Jets. (arXiv:1209.5748v1 [astro-ph.CO])
Isotropic Heating of Galaxy Cluster Cores via Rapidly Reorienting AGN Jets. (arXiv:1209.5748v1 [astro-ph.CO]):
AGN jets carry more than sufficient energy to stave off catastrophic cooling
of the intracluster medium (ICM) in the cores of cool-core clusters. However,
in order to prevent catastrophic cooling, the ICM must be heated in a
near-isotropic fashion and narrow bipolar jets are inefficient at heating the
gas in the transverse direction to the jets. We argue that due to existent
conditions in cluster cores, the SMBHs will, in addition to accreting gas via
radiatively inefficient flows, experience short stochastic episodes of enhanced
accretion via thin discs. In general, the orientation of these accretion discs
will be misaligned with the spin axis of the black holes and the ensuing
torques will cause the black hole's spin axis (and therefore, the jet axis) to
slew and rapidly change direction. This model not only explains recent
observations showing successive generations of jet-lobes-bubbles in individual
cool-core clusters that are offset from each other in the angular direction
with respect to the cluster center, but also shows that AGN jets {\it can} heat
the cluster core nearly isotropically on the gas cooling timescale. One
implication of our proposed model is that since SMBHs that host thin accretion
discs will manifest as quasars, we predicts that roughly 1--2 rich clusters
within $z<0.5$ should have quasars at their centers. Also, recurrent accretion
via misaligned accretion discs implies that as a population, the SMBHs at the
centers of cool-core clusters should be spinning slowly. Our model, in fact,
requires SMBHs to be spinning slowly. Torques from misaligned discs are
ineffective at tilting rapidly spinning black holes by more a few degrees
whereas slowly spinning SMBHs can, under optimal conditions, slew by as much as
$\sim 30^\circ$ during any one accretion event.
AGN jets carry more than sufficient energy to stave off catastrophic cooling
of the intracluster medium (ICM) in the cores of cool-core clusters. However,
in order to prevent catastrophic cooling, the ICM must be heated in a
near-isotropic fashion and narrow bipolar jets are inefficient at heating the
gas in the transverse direction to the jets. We argue that due to existent
conditions in cluster cores, the SMBHs will, in addition to accreting gas via
radiatively inefficient flows, experience short stochastic episodes of enhanced
accretion via thin discs. In general, the orientation of these accretion discs
will be misaligned with the spin axis of the black holes and the ensuing
torques will cause the black hole's spin axis (and therefore, the jet axis) to
slew and rapidly change direction. This model not only explains recent
observations showing successive generations of jet-lobes-bubbles in individual
cool-core clusters that are offset from each other in the angular direction
with respect to the cluster center, but also shows that AGN jets {\it can} heat
the cluster core nearly isotropically on the gas cooling timescale. One
implication of our proposed model is that since SMBHs that host thin accretion
discs will manifest as quasars, we predicts that roughly 1--2 rich clusters
within $z<0.5$ should have quasars at their centers. Also, recurrent accretion
via misaligned accretion discs implies that as a population, the SMBHs at the
centers of cool-core clusters should be spinning slowly. Our model, in fact,
requires SMBHs to be spinning slowly. Torques from misaligned discs are
ineffective at tilting rapidly spinning black holes by more a few degrees
whereas slowly spinning SMBHs can, under optimal conditions, slew by as much as
$\sim 30^\circ$ during any one accretion event.
Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*. (arXiv:1209.6354v1 [astro-ph.HE])
Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*. (arXiv:1209.6354v1 [astro-ph.HE]):
Starting in 2012, we began an unprecedented observational program focused on
the supermassive black hole in the center of our Galaxy, Sgr A*, utilizing the
High Energy Transmission Gratings Spectrometer (HETGS) instrument on the
Chandra X-ray Observatory. These observations will allow us to measure the
quiescent X-ray spectra of Sgr A* for the first time at both high spatial and
spectral resolution. The X-ray emission of Sgr A*, however, is known to flare
roughly daily by factors of a few to ten times over quiescent emission levels,
with rarer flares extending to factors of greater than 100 times quiescence.
Here were report an observation performed on 2012 February 9 wherein we
detected what is the highest peak flux and fluence flare ever observed from Sgr
A*. The flare, which lasted for 5.6 ks and had a decidedly asymmetric profile
with a faster decline than rise, achieved a mean absorbed 2-8 keV flux of
(8.5+/-0.9)X10^{-12} erg cm^{-2} s^{-1}. The peak flux was 2.5 times higher,
and the total 2-10 keV emission of the event was approximately 10^{39} erg.
Only one other flare of comparable magnitude, but shorter duration, has been
observed in Sgr A* by XMM-Newton in 2002 October. We perform spectral fits of
this Chandra observed flare, and compare our results to the two brightest
flares ever observed with XMM-Newton. We find good agreement among the fitted
spectral slopes (Gamma~2) and X-ray absorbing columns (N_H~15X10^{22} cm^{-2})
for all three of these events, resolving prior differences (which are most
likely due to the combined effects of pileup and spectral modeling) among
Chandra and XMM-Newton observations of Sgr A* flares. We also discuss fits to
the quiescent spectra of Sgr A*.
Starting in 2012, we began an unprecedented observational program focused on
the supermassive black hole in the center of our Galaxy, Sgr A*, utilizing the
High Energy Transmission Gratings Spectrometer (HETGS) instrument on the
Chandra X-ray Observatory. These observations will allow us to measure the
quiescent X-ray spectra of Sgr A* for the first time at both high spatial and
spectral resolution. The X-ray emission of Sgr A*, however, is known to flare
roughly daily by factors of a few to ten times over quiescent emission levels,
with rarer flares extending to factors of greater than 100 times quiescence.
Here were report an observation performed on 2012 February 9 wherein we
detected what is the highest peak flux and fluence flare ever observed from Sgr
A*. The flare, which lasted for 5.6 ks and had a decidedly asymmetric profile
with a faster decline than rise, achieved a mean absorbed 2-8 keV flux of
(8.5+/-0.9)X10^{-12} erg cm^{-2} s^{-1}. The peak flux was 2.5 times higher,
and the total 2-10 keV emission of the event was approximately 10^{39} erg.
Only one other flare of comparable magnitude, but shorter duration, has been
observed in Sgr A* by XMM-Newton in 2002 October. We perform spectral fits of
this Chandra observed flare, and compare our results to the two brightest
flares ever observed with XMM-Newton. We find good agreement among the fitted
spectral slopes (Gamma~2) and X-ray absorbing columns (N_H~15X10^{22} cm^{-2})
for all three of these events, resolving prior differences (which are most
likely due to the combined effects of pileup and spectral modeling) among
Chandra and XMM-Newton observations of Sgr A* flares. We also discuss fits to
the quiescent spectra of Sgr A*.
Clustering, Bias and the Accretion Mode of X-ray selected AGN. (arXiv:1209.6460v1 [astro-ph.CO])
Clustering, Bias and the Accretion Mode of X-ray selected AGN. (arXiv:1209.6460v1 [astro-ph.CO]):
We present the spatial clustering properties of 1466 X-ray selected AGN
compiled from the Chandra CDF-N, CDF-S, eCDF-S, COSMOS and AEGIS fields in the
0.5-8 keV band. The X-ray sources span the redshift interval 0<z<3 and have a
median value of Med{z}=0.976.We employ the projected two-point correlation
function to infer the spatial clustering and find a clustering length of r0=
7.2+-0.6 h^{-1} Mpc and a slope of \gamma=1.48+-0.12, which corresponds to a
bias of b=2.26+-0.16. Using two different halo bias models, we consistently
estimate an average dark-matter host halo mass of Mh\sim 1.3 (+-0.3) x 10^{13}
h^{-1} M_sun. The X-ray AGN bias and the corresponding dark-matter host halo
mass, are significantly higher than the corresponding values of optically
selected AGN (at the same redshifts). %indicating different populations of AGN.
The redshift evolution of the X-ray selected AGN bias indicates, in agreement
with other recent studies, that a unique dark-matter halo mass does not fit
well the bias at all the different redshifts probed.
Furthermore, we investigate if there is a dependence of the clustering
strength on X-ray luminosity. To this end we consider only 650 sources around
z~1 and we apply a procedure to disentangle the dependence of clustering on
redshift. We find indications for a positive dependence of the clustering
length on X-ray luminosity, in the sense that the more luminous sources have a
larger clustering length and hence a higher dark-matter halo mass. In detail we
find for an average luminosity difference of \delta\log_{10} L_x ~ 1 a halo
mass difference of a factor of ~3.
These findings appear to be consistent with a galaxy-formation model where
the gas accreted onto the supermassive black hole in intermediate luminosity
AGN comes mostly from the hot-halo atmosphere around the host galaxy.
We present the spatial clustering properties of 1466 X-ray selected AGN
compiled from the Chandra CDF-N, CDF-S, eCDF-S, COSMOS and AEGIS fields in the
0.5-8 keV band. The X-ray sources span the redshift interval 0<z<3 and have a
median value of Med{z}=0.976.We employ the projected two-point correlation
function to infer the spatial clustering and find a clustering length of r0=
7.2+-0.6 h^{-1} Mpc and a slope of \gamma=1.48+-0.12, which corresponds to a
bias of b=2.26+-0.16. Using two different halo bias models, we consistently
estimate an average dark-matter host halo mass of Mh\sim 1.3 (+-0.3) x 10^{13}
h^{-1} M_sun. The X-ray AGN bias and the corresponding dark-matter host halo
mass, are significantly higher than the corresponding values of optically
selected AGN (at the same redshifts). %indicating different populations of AGN.
The redshift evolution of the X-ray selected AGN bias indicates, in agreement
with other recent studies, that a unique dark-matter halo mass does not fit
well the bias at all the different redshifts probed.
Furthermore, we investigate if there is a dependence of the clustering
strength on X-ray luminosity. To this end we consider only 650 sources around
z~1 and we apply a procedure to disentangle the dependence of clustering on
redshift. We find indications for a positive dependence of the clustering
length on X-ray luminosity, in the sense that the more luminous sources have a
larger clustering length and hence a higher dark-matter halo mass. In detail we
find for an average luminosity difference of \delta\log_{10} L_x ~ 1 a halo
mass difference of a factor of ~3.
These findings appear to be consistent with a galaxy-formation model where
the gas accreted onto the supermassive black hole in intermediate luminosity
AGN comes mostly from the hot-halo atmosphere around the host galaxy.
A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc])
A Metric for Testing the Nature of Black Holes. (arXiv:1210.0483v1 [gr-qc]):
In general relativity, astrophysical black holes are uniquely described by
the Kerr metric. Observational tests of the Kerr nature of these compact
objects and, hence, of general relativity, require a metric that encompasses a
broader class of black holes as possible alternatives to the usual Kerr black
holes. Several such Kerr-like metrics have been constructed to date, which
depend on a set of free parameters and which reduce smoothly to the Kerr metric
if all deviations vanish. Many of these metrics, however, are valid only for
small values of the spin or small perturbations of the Kerr metric or contain
regions of space where they are unphysical hampering their ability to properly
model the accretions flows of black holes. In this paper, I describe a
Kerr-like black hole metric that is regular everywhere outside of the event
horizon for black holes with arbitrary spins even for large deviations from the
Kerr metric. This metric, therefore, provides an ideal framework for tests of
the nature of black holes with observations of the emission from their
accretion flows, and I give several examples of such tests across the
electromagnetic spectrum with current and near-future instruments.
Note: This paper notes how broadened Fe-K lines could test the black hole 'No-Hair' Theorem, with predictions of line shapes.
In general relativity, astrophysical black holes are uniquely described by
the Kerr metric. Observational tests of the Kerr nature of these compact
objects and, hence, of general relativity, require a metric that encompasses a
broader class of black holes as possible alternatives to the usual Kerr black
holes. Several such Kerr-like metrics have been constructed to date, which
depend on a set of free parameters and which reduce smoothly to the Kerr metric
if all deviations vanish. Many of these metrics, however, are valid only for
small values of the spin or small perturbations of the Kerr metric or contain
regions of space where they are unphysical hampering their ability to properly
model the accretions flows of black holes. In this paper, I describe a
Kerr-like black hole metric that is regular everywhere outside of the event
horizon for black holes with arbitrary spins even for large deviations from the
Kerr metric. This metric, therefore, provides an ideal framework for tests of
the nature of black holes with observations of the emission from their
accretion flows, and I give several examples of such tests across the
electromagnetic spectrum with current and near-future instruments.
Note: This paper notes how broadened Fe-K lines could test the black hole 'No-Hair' Theorem, with predictions of line shapes.
Direct Measurement of the X-ray Time-Delay Transfer Function in Active Galactic Nuclei. (arXiv:1210.0469v1 [astro-ph.HE])
Direct Measurement of the X-ray Time-Delay Transfer Function in Active Galactic Nuclei. (arXiv:1210.0469v1 [astro-ph.HE]):
The origin of the observed time lags, in nearby active galactic nuclei (AGN),
between hard and soft X-ray photons is investigated using new XMM-Newton data
for the narrow-line Seyfert I galaxy Ark 564 and existing data for 1H0707-495
and NGC 4051. These AGN have highly variable X-ray light curves that contain
frequent, high peaks of emission. The averaged light curve of the peaks is
directly measured from the time series, and it is shown that (i) peaks occur at
the same time, within the measurement uncertainties, at all X-ray energies, and
(ii) there exists a substantial tail of excess emission at hard X-ray energies,
which is delayed with respect to the time of the main peak, and is particularly
prominent in Ark 564. Observation (i) rules out that the observed lags are
caused by Comptonization time delays and disfavors a simple model of
propagating fluctuations on the accretion disk. Observation (ii) is consistent
with time lags caused by Compton-scattering reverberation from material a few
thousand light-seconds from the primary X-ray source. The power spectral
density and the frequency-dependent phase lags of the peak light curves are
consistent with those of the full time series. There is evidence for
non-stationarity in the Ark 564 time series in both the Fourier and peaks
analyses. A sharp `negative' lag (variations at hard photon energies lead soft
photon energies) observed in Ark 564 appears to be generated by the shape of
the hard-band transfer function and does not arise from soft-band reflection of
X-rays. These results reinforce the evidence for the existence of X-ray
reverberation in type I AGN, which requires that these AGN are significantly
affected by scattering from circumnuclear material a few tens or hundreds of
gravitational radii in extent.
The origin of the observed time lags, in nearby active galactic nuclei (AGN),
between hard and soft X-ray photons is investigated using new XMM-Newton data
for the narrow-line Seyfert I galaxy Ark 564 and existing data for 1H0707-495
and NGC 4051. These AGN have highly variable X-ray light curves that contain
frequent, high peaks of emission. The averaged light curve of the peaks is
directly measured from the time series, and it is shown that (i) peaks occur at
the same time, within the measurement uncertainties, at all X-ray energies, and
(ii) there exists a substantial tail of excess emission at hard X-ray energies,
which is delayed with respect to the time of the main peak, and is particularly
prominent in Ark 564. Observation (i) rules out that the observed lags are
caused by Comptonization time delays and disfavors a simple model of
propagating fluctuations on the accretion disk. Observation (ii) is consistent
with time lags caused by Compton-scattering reverberation from material a few
thousand light-seconds from the primary X-ray source. The power spectral
density and the frequency-dependent phase lags of the peak light curves are
consistent with those of the full time series. There is evidence for
non-stationarity in the Ark 564 time series in both the Fourier and peaks
analyses. A sharp `negative' lag (variations at hard photon energies lead soft
photon energies) observed in Ark 564 appears to be generated by the shape of
the hard-band transfer function and does not arise from soft-band reflection of
X-rays. These results reinforce the evidence for the existence of X-ray
reverberation in type I AGN, which requires that these AGN are significantly
affected by scattering from circumnuclear material a few tens or hundreds of
gravitational radii in extent.
A blurred reflection interpretation for the intermediate flux state in Mrk 335. (arXiv:1210.0855v1 [astro-ph.HE])
A blurred reflection interpretation for the intermediate flux state in Mrk 335. (arXiv:1210.0855v1 [astro-ph.HE]):
As part of a long term monitoring campaign of Mrk 335, deep XMM-Newton
observations catch the narrow-line Seyfert 1 galaxy (NLS1) in a complex,
intermediate flux interval as the active galaxy is transiting from low- to
high-flux. Other works on these same data examined the general behaviour of the
NLS1 (Grupe et al.) and the conditions of its warm absorber (Longinotti et
al.). The analysis presented here demonstrates the X-ray continuum and timing
properties can be described in a self-consistent manner adopting a blurred
reflection model with no need to invoke partial covering. The rapid spectral
variability appears to be driven by changes in the shape of the primary emitter
that is illuminating the inner accretion disc around a rapidly spinning black
hole (a > 0.7). While light bending is certainly prominent, the rather constant
emissivity profile and break radius obtained in our spectral fitting suggest
that the blurring parameters are not changing as would be expected if the
primary source is varying its distance from the disc. Instead changes could be
intrinsic to the power law component. One possibility is that material in an
unresolved jet above the disc falls to combine with material at the base of the
jet producing the changes in the primary emitter (spectral slope and flux)
without changing its distance from the disc.
As part of a long term monitoring campaign of Mrk 335, deep XMM-Newton
observations catch the narrow-line Seyfert 1 galaxy (NLS1) in a complex,
intermediate flux interval as the active galaxy is transiting from low- to
high-flux. Other works on these same data examined the general behaviour of the
NLS1 (Grupe et al.) and the conditions of its warm absorber (Longinotti et
al.). The analysis presented here demonstrates the X-ray continuum and timing
properties can be described in a self-consistent manner adopting a blurred
reflection model with no need to invoke partial covering. The rapid spectral
variability appears to be driven by changes in the shape of the primary emitter
that is illuminating the inner accretion disc around a rapidly spinning black
hole (a > 0.7). While light bending is certainly prominent, the rather constant
emissivity profile and break radius obtained in our spectral fitting suggest
that the blurring parameters are not changing as would be expected if the
primary source is varying its distance from the disc. Instead changes could be
intrinsic to the power law component. One possibility is that material in an
unresolved jet above the disc falls to combine with material at the base of the
jet producing the changes in the primary emitter (spectral slope and flux)
without changing its distance from the disc.
The origin of the chemical elements in cluster cores. (arXiv:1210.1093v1 [astro-ph.CO])
The origin of the chemical elements in cluster cores. (arXiv:1210.1093v1 [astro-ph.CO]):
Metals play a fundamental role in ICM cooling processes in cluster cores
through the emission of spectral lines. But when and how were these metals
formed and distributed through the ICM? The X-ray band has the unique property
of containing emission lines from all elements from carbon to zinc within the
0.1-10 keV band. Using XMM-Newton, the abundances of about 11 elements are
studied, which contain valuable information about their origin. Most elements
were formed in type Ia and core-collapse supernovae, which have very different
chemical yields. Massive stars and AGB stars also contribute by providing most
of the carbon and nitrogen in the ICM. Because feedback processes suppress star
formation in the cluster centre, the element abundances allow us to directly
probe the star formation history of the majority of stars that are thought to
have formed between z=2-3. The spatial distribution in the core and the
evolution with redshift also provide information about how these elements are
transported from the member galaxies to the ICM. I review the current progress
in chemical enrichment studies of the ICM and give an outlook to the future
opportunities provided by XMM-Newton's successors, like Astro-H.
Metals play a fundamental role in ICM cooling processes in cluster cores
through the emission of spectral lines. But when and how were these metals
formed and distributed through the ICM? The X-ray band has the unique property
of containing emission lines from all elements from carbon to zinc within the
0.1-10 keV band. Using XMM-Newton, the abundances of about 11 elements are
studied, which contain valuable information about their origin. Most elements
were formed in type Ia and core-collapse supernovae, which have very different
chemical yields. Massive stars and AGB stars also contribute by providing most
of the carbon and nitrogen in the ICM. Because feedback processes suppress star
formation in the cluster centre, the element abundances allow us to directly
probe the star formation history of the majority of stars that are thought to
have formed between z=2-3. The spatial distribution in the core and the
evolution with redshift also provide information about how these elements are
transported from the member galaxies to the ICM. I review the current progress
in chemical enrichment studies of the ICM and give an outlook to the future
opportunities provided by XMM-Newton's successors, like Astro-H.
The evolution of active galactic nuclei and their spins. (arXiv:1210.1025v1 [astro-ph.HE])
The evolution of active galactic nuclei and their spins. (arXiv:1210.1025v1 [astro-ph.HE]):
Massive black holes (MBHs) in contrast to stellar mass black holes are
expected to substantially change their properties over their lifetime. MBH
masses increase by several order of magnitude over the Hubble time, as
illustrated by Soltan's argument. MBH spins also must evolve through the series
of accretion and mergers events that grow the MBH's masses. We present a simple
model that traces the joint evolution of MBH masses and spins across cosmic
time. Our model includes MBH-MBH mergers, merger-driven gas accretion,
stochastic fueling of MBHs through molecular cloud capture, and a basic
implementation of accretion of recycled gas. This approach aims at improving
the modeling of low-redshift MBHs and AGN, whose properties can be more easily
estimated observationally. Despite the simplicity of the model, it captures
well the global evolution of the MBH population from z\sim6 to today. Under our
assumptions, we find that the typical spin and radiative efficiency of MBHs
decrease with cosmic time because of the higher incidence of stochastic
processes in gas-rich galaxies and MBH-MBH mergers in gas-poor galaxies. At z=0
the spin distribution in gas-poor galaxies peaks at spins 0.4-0.8, and it is
not strongly mass dependent. MBHs in gas-rich galaxies have a more complex
evolution, with low-mass MBHs at low redshift having low spins, and spins
increasing at larger masses and redshifts. We also find that at z>1 MBH spins
are on average highest in high luminosity AGN, while at lower redshifts these
differences disappear.
Massive black holes (MBHs) in contrast to stellar mass black holes are
expected to substantially change their properties over their lifetime. MBH
masses increase by several order of magnitude over the Hubble time, as
illustrated by Soltan's argument. MBH spins also must evolve through the series
of accretion and mergers events that grow the MBH's masses. We present a simple
model that traces the joint evolution of MBH masses and spins across cosmic
time. Our model includes MBH-MBH mergers, merger-driven gas accretion,
stochastic fueling of MBHs through molecular cloud capture, and a basic
implementation of accretion of recycled gas. This approach aims at improving
the modeling of low-redshift MBHs and AGN, whose properties can be more easily
estimated observationally. Despite the simplicity of the model, it captures
well the global evolution of the MBH population from z\sim6 to today. Under our
assumptions, we find that the typical spin and radiative efficiency of MBHs
decrease with cosmic time because of the higher incidence of stochastic
processes in gas-rich galaxies and MBH-MBH mergers in gas-poor galaxies. At z=0
the spin distribution in gas-poor galaxies peaks at spins 0.4-0.8, and it is
not strongly mass dependent. MBHs in gas-rich galaxies have a more complex
evolution, with low-mass MBHs at low redshift having low spins, and spins
increasing at larger masses and redshifts. We also find that at z>1 MBH spins
are on average highest in high luminosity AGN, while at lower redshifts these
differences disappear.
Effect of superfluidity on neutron star crustal oscillations. (arXiv:1210.0955v1 [astro-ph.HE])
Effect of superfluidity on neutron star crustal oscillations. (arXiv:1210.0955v1 [astro-ph.HE]):
We consider how superfluidity of dripped neutrons in the crust of a neutron
star affects the frequencies of the crust's fundamental torsional oscillations.
A nonnegligible superfluid part of dripped neutrons, which do not comove with
nuclei, act to reduce the enthalpy density and thus enhance the oscillation
frequencies. By assuming that the quasi-periodic oscillations observed in giant
flares of soft gamma repeaters arise from the fundamental torsional
oscillations and that the mass and radius of the neutron star is in the range
of 1.4 < M/M_SUN < 1.8 and 10 km < R < 14 km, we constrain the density
derivative of the symmetry energy as 100 MeV < L < 130 MeV, which is far
severer than the previous one, L > 50 MeV, derived by ignoring the
superfluidity.
We consider how superfluidity of dripped neutrons in the crust of a neutron
star affects the frequencies of the crust's fundamental torsional oscillations.
A nonnegligible superfluid part of dripped neutrons, which do not comove with
nuclei, act to reduce the enthalpy density and thus enhance the oscillation
frequencies. By assuming that the quasi-periodic oscillations observed in giant
flares of soft gamma repeaters arise from the fundamental torsional
oscillations and that the mass and radius of the neutron star is in the range
of 1.4 < M/M_SUN < 1.8 and 10 km < R < 14 km, we constrain the density
derivative of the symmetry energy as 100 MeV < L < 130 MeV, which is far
severer than the previous one, L > 50 MeV, derived by ignoring the
superfluidity.
Surface Emission from Neutron Stars and Implications for the Physics of their Interiors. (arXiv:1210.0916v1 [astro-ph.HE])
Surface Emission from Neutron Stars and Implications for the Physics of their Interiors. (arXiv:1210.0916v1 [astro-ph.HE]):
Neutron stars are associated with diverse physical phenomena that take place
in conditions characterized by ultrahigh densities as well as intense
gravitational, magnetic, and radiation fields. Understanding the properties and
interactions of matter in these regimes remains one of the challenges in
compact object astrophysics. Photons emitted from the surfaces of neutron stars
provide direct probes of their structure, composition, and magnetic fields. In
this review, I discuss in detail the physics that governs the properties of
emission from the surfaces of neutron stars and their various observational
manifestations. I present the constraints on neutron star radii, core and crust
composition, and magnetic field strength and topology obtained from studies of
their broadband spectra, evolution of thermal luminosity, and the profiles of
pulsations that originate on their surfaces.
Neutron stars are associated with diverse physical phenomena that take place
in conditions characterized by ultrahigh densities as well as intense
gravitational, magnetic, and radiation fields. Understanding the properties and
interactions of matter in these regimes remains one of the challenges in
compact object astrophysics. Photons emitted from the surfaces of neutron stars
provide direct probes of their structure, composition, and magnetic fields. In
this review, I discuss in detail the physics that governs the properties of
emission from the surfaces of neutron stars and their various observational
manifestations. I present the constraints on neutron star radii, core and crust
composition, and magnetic field strength and topology obtained from studies of
their broadband spectra, evolution of thermal luminosity, and the profiles of
pulsations that originate on their surfaces.
Two stellar-mass black holes in the globular cluster M22. (arXiv:1210.0901v1 [astro-ph.HE])
Two stellar-mass black holes in the globular cluster M22. (arXiv:1210.0901v1 [astro-ph.HE]):
Hundreds of stellar-mass black holes likely form in a typical globular star
cluster, with all but one predicted to be ejected through dynamical
interactions. Some observational support for this idea is provided by the lack
of X-ray-emitting binary stars comprising one black hole and one other star
("black-hole/X-ray binaries") in Milky Way globular clusters, even though many
neutron-star/X-ray binaries are known. Although a few black holes have been
seen in globular clusters around other galaxies, the masses of these cannot be
determined, and some may be intermediate-mass black holes that form through
exotic mechanisms. Here we report the presence of two flat-spectrum radio
sources in the Milky Way globular cluster M22, and we argue that these objects
are black holes of stellar mass (each ~ 10-20 times more massive than the Sun)
that are accreting matter. We find a high ratio of radio-to-X-ray flux for
these black holes, consistent with the larger predicted masses of black holes
in globular clusters compared to those outside. The identification of two black
holes in one cluster shows that the ejection of black holes is not as efficient
as predicted by most models, and we argue that M22 may contain a total
population of ~ 5-100 black holes. The large core radius of M22 could arise
from heating produced by the black holes.
Hundreds of stellar-mass black holes likely form in a typical globular star
cluster, with all but one predicted to be ejected through dynamical
interactions. Some observational support for this idea is provided by the lack
of X-ray-emitting binary stars comprising one black hole and one other star
("black-hole/X-ray binaries") in Milky Way globular clusters, even though many
neutron-star/X-ray binaries are known. Although a few black holes have been
seen in globular clusters around other galaxies, the masses of these cannot be
determined, and some may be intermediate-mass black holes that form through
exotic mechanisms. Here we report the presence of two flat-spectrum radio
sources in the Milky Way globular cluster M22, and we argue that these objects
are black holes of stellar mass (each ~ 10-20 times more massive than the Sun)
that are accreting matter. We find a high ratio of radio-to-X-ray flux for
these black holes, consistent with the larger predicted masses of black holes
in globular clusters compared to those outside. The identification of two black
holes in one cluster shows that the ejection of black holes is not as efficient
as predicted by most models, and we argue that M22 may contain a total
population of ~ 5-100 black holes. The large core radius of M22 could arise
from heating produced by the black holes.
Low-frequency QPO from the 11 Hz accreting pulsar in Terzan 5: not frame dragging. (arXiv:1210.1494v1 [astro-ph.HE])
Low-frequency QPO from the 11 Hz accreting pulsar in Terzan 5: not frame dragging. (arXiv:1210.1494v1 [astro-ph.HE]):
We report on 6 RXTE observations taken during the 2010 outburst of the 11 Hz
accreting pulsar IGR J17480-2446 located in the globular cluster Terzan 5.
During these observations we find power spectra which resemble those seen in
Z-type high-luminosity neutron star low-mass X-ray binaries, with a
quasi-periodic oscillation (QPO) in the 35-50 Hz range simultaneous with a kHz
QPO and broad band noise. Using well known frequency-frequency correlations, we
identify the 35-50 Hz QPOs as the horizontal branch oscillations (HBO), which
were previously suggested to be due to Lense-Thirring precession. As IGR
J17480-2446 spins more than an order of magnitude more slowly than any of the
other neutron stars where these QPOs were found, this QPO can not be explained
by frame dragging. By extension, this casts doubt on the Lense-Thirring
precession model for other low-frequency QPOs in neutron-star and perhaps even
black-hole systems.
We report on 6 RXTE observations taken during the 2010 outburst of the 11 Hz
accreting pulsar IGR J17480-2446 located in the globular cluster Terzan 5.
During these observations we find power spectra which resemble those seen in
Z-type high-luminosity neutron star low-mass X-ray binaries, with a
quasi-periodic oscillation (QPO) in the 35-50 Hz range simultaneous with a kHz
QPO and broad band noise. Using well known frequency-frequency correlations, we
identify the 35-50 Hz QPOs as the horizontal branch oscillations (HBO), which
were previously suggested to be due to Lense-Thirring precession. As IGR
J17480-2446 spins more than an order of magnitude more slowly than any of the
other neutron stars where these QPOs were found, this QPO can not be explained
by frame dragging. By extension, this casts doubt on the Lense-Thirring
precession model for other low-frequency QPOs in neutron-star and perhaps even
black-hole systems.
The Closest Look at 1H0707-495: X-ray Reverberation Lags with 1.3 Ms of Data. (arXiv:1210.1465v1 [astro-ph.HE])
The Closest Look at 1H0707-495: X-ray Reverberation Lags with 1.3 Ms of Data. (arXiv:1210.1465v1 [astro-ph.HE]):
Reverberation lags in AGN were first discovered in the NLS1 galaxy,
1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows
for the closest ever look at the reverberation signature of this remarkable
source. We confirm previous findings of a hard lag of ~100 seconds at
frequencies v ~ [0.5 - 4] e-4 Hz, and a soft lag of ~30 seconds at higher
frequencies, v ~ [0.6 - 3] e-3 Hz. These two frequency domains clearly show
different energy dependences in their lag spectra. We also find evidence for a
signature from the broad Fe K line in the high frequency lag spectrum. We use
Monte Carlo simulations to show how the lag and coherence measurements respond
to the addition of Poisson noise and to dilution by other components. With our
better understanding of these effects on the lag, we show that the lag-energy
spectra can be modelled with a scenario in which low frequency hard lags are
produced by a compact corona responding to accretion rate fluctuations
propagating through an optically thick accretion disc, and the high frequency
soft lags are produced by short light-travel delay associated with reflection
of coronal power-law photons off the disc.
Reverberation lags in AGN were first discovered in the NLS1 galaxy,
1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows
for the closest ever look at the reverberation signature of this remarkable
source. We confirm previous findings of a hard lag of ~100 seconds at
frequencies v ~ [0.5 - 4] e-4 Hz, and a soft lag of ~30 seconds at higher
frequencies, v ~ [0.6 - 3] e-3 Hz. These two frequency domains clearly show
different energy dependences in their lag spectra. We also find evidence for a
signature from the broad Fe K line in the high frequency lag spectrum. We use
Monte Carlo simulations to show how the lag and coherence measurements respond
to the addition of Poisson noise and to dilution by other components. With our
better understanding of these effects on the lag, we show that the lag-energy
spectra can be modelled with a scenario in which low frequency hard lags are
produced by a compact corona responding to accretion rate fluctuations
propagating through an optically thick accretion disc, and the high frequency
soft lags are produced by short light-travel delay associated with reflection
of coronal power-law photons off the disc.
Temperature, Abundance, and Mass Density Profiling of the Perseus Galaxy Cluster. (arXiv:1210.1253v1 [astro-ph.CO])
Temperature, Abundance, and Mass Density Profiling of the Perseus Galaxy Cluster. (arXiv:1210.1253v1 [astro-ph.CO]):
Detailed temperature and abundance radial profile maps have revealed a
significant lack of homogeneity within the Perseus Galaxy cluster. Previous
surveys of Perseus with the Suzaku telescope, which has a worse angular
resolution and less light collecting area than XMM-Newton, revealed
over-densities of X-Ray emission. These results provide evidence that the
baryon fraction exceeds the universal average, which we had initially hoped to
study. We have yet to confirm or deny the existence of clumping in these
regions, which could explain such over-abundance of X-Ray emission. This
project offers a framework of efficient, automated processing techniques to
"clean" images of noise from the mechanics of the telescope, background
radiation from local sources such as the solar wind, and more distant sources
such as background AGN. The galaxy cluster studied in this project contains
high levels of contamination due to its line-of-sight position close to the
dust- and star-filled arms of the Milky Way galaxy. Rigorous spectral model
fitting of the cluster employ multiple parameters dedicated to accounting for
these contaminations. The framework created from this analysis technique will
provide the opportunity to expand this analysis to any nearby galaxy cluster,
such as the Virgo, Coma, and Ophiuchus Clusters. This research should provide
significant insight into how matter, both baryonic and dark matter, is
distributed throughout diffuse cluster systems, as well as give clues to the
origin of the ICM.
Detailed temperature and abundance radial profile maps have revealed a
significant lack of homogeneity within the Perseus Galaxy cluster. Previous
surveys of Perseus with the Suzaku telescope, which has a worse angular
resolution and less light collecting area than XMM-Newton, revealed
over-densities of X-Ray emission. These results provide evidence that the
baryon fraction exceeds the universal average, which we had initially hoped to
study. We have yet to confirm or deny the existence of clumping in these
regions, which could explain such over-abundance of X-Ray emission. This
project offers a framework of efficient, automated processing techniques to
"clean" images of noise from the mechanics of the telescope, background
radiation from local sources such as the solar wind, and more distant sources
such as background AGN. The galaxy cluster studied in this project contains
high levels of contamination due to its line-of-sight position close to the
dust- and star-filled arms of the Milky Way galaxy. Rigorous spectral model
fitting of the cluster employ multiple parameters dedicated to accounting for
these contaminations. The framework created from this analysis technique will
provide the opportunity to expand this analysis to any nearby galaxy cluster,
such as the Virgo, Coma, and Ophiuchus Clusters. This research should provide
significant insight into how matter, both baryonic and dark matter, is
distributed throughout diffuse cluster systems, as well as give clues to the
origin of the ICM.
Wednesday, October 3, 2012
Ab initio calculations on nuclear matter properties including the effects of three-nucleons interaction. (arXiv:1210.0593v1 [nucl-th])
Ab initio calculations on nuclear matter properties including the effects of three-nucleons interaction. (arXiv:1210.0593v1 [nucl-th]):
In this thesis, the ground state properties of nuclear matter, namely the
energy per particle and the response to weak probes, are computed, studying the
effects of three nucleon interactions. Both the variational approach, based on
the formalism of correlated basis function, and the auxiliary field diffusion
Monte Carlo method have been used. A scheme suitable to construct a
density-dependent two-nucleon potential in correlated basis approach is
discussed. The density dependent potential resulting from UIX three-nucleon
force has been employed in auxiliary field diffusion Monte Carlo calculations
that turned out to be in very good agreement with correlated basis variational
results. Hence, the underbinding of symmetric nuclear matter has to be ascribed
to deficiencies of the UXI potential. A comparative analysis of the equations
of state of both pure neutron matter and symmetric nuclear matter obtained
using a new generation of "chiral inspired" local three-body potentials has
been performed. These potentials provide an excellent description of the
properties of light nuclei, as well as of the neutron-deuteron doublet
scattering length. The weak response of symmetric nuclear matter has been
computed at three-body cluster level. Two-body effective interactions and
one-body effective operators have been derived within the formalism of
correlated basis functions. The inclusion of the three-body cluster term in the
effective interaction allowed for a direct inclusion of the UIX three-nucleon
potential. Moreover, the sizable unphysical dependence of the effective weak
operator is removed once the three-body cluster term is taken into account.
In this thesis, the ground state properties of nuclear matter, namely the
energy per particle and the response to weak probes, are computed, studying the
effects of three nucleon interactions. Both the variational approach, based on
the formalism of correlated basis function, and the auxiliary field diffusion
Monte Carlo method have been used. A scheme suitable to construct a
density-dependent two-nucleon potential in correlated basis approach is
discussed. The density dependent potential resulting from UIX three-nucleon
force has been employed in auxiliary field diffusion Monte Carlo calculations
that turned out to be in very good agreement with correlated basis variational
results. Hence, the underbinding of symmetric nuclear matter has to be ascribed
to deficiencies of the UXI potential. A comparative analysis of the equations
of state of both pure neutron matter and symmetric nuclear matter obtained
using a new generation of "chiral inspired" local three-body potentials has
been performed. These potentials provide an excellent description of the
properties of light nuclei, as well as of the neutron-deuteron doublet
scattering length. The weak response of symmetric nuclear matter has been
computed at three-body cluster level. Two-body effective interactions and
one-body effective operators have been derived within the formalism of
correlated basis functions. The inclusion of the three-body cluster term in the
effective interaction allowed for a direct inclusion of the UIX three-nucleon
potential. Moreover, the sizable unphysical dependence of the effective weak
operator is removed once the three-body cluster term is taken into account.
Finding Rare AGN: X-ray Number Counts of Chandra Sources in Stripe 82. (arXiv:1210.0550v1 [astro-ph.CO])
Finding Rare AGN: X-ray Number Counts of Chandra Sources in Stripe 82. (arXiv:1210.0550v1 [astro-ph.CO]):
We present the first results of a wide area X-ray survey within the Sloan
Digital Sky Survey (SDSS) Stripe 82, a 300 deg$^2$ region of the sky with a
substantial investment in multi-wavelength coverage. We analyzed archival {\it
Chandra} observations that cover 7.5 deg$^2$ within Stripe 82 ("Stripe 82
ACX"), reaching 4.5$\sigma$ flux limits of 7.9$\times10^{-16}$,
3.4$\times10^{-15}$ and 1.8$\times10^{-15}$ erg s$^{-1}$ cm$^{-2}$ in the soft
(0.5-2 keV), hard (2-7 keV) and full (0.5-7 keV) bands, to find 774, 239 and
1118 X-ray sources, respectively. Three hundred twenty-one sources are detected
only in the full band and 9 sources are detected solely in the soft band.
Utilizing data products from the {\it Chandra} Source Catalog, we construct
independent Log$N$-Log$S$ relationships, detailing the number density of X-ray
sources as a function of flux, which show general agreement with previous {\it
Chandra} surveys. We compare the luminosity distribution of Stripe 82 ACX with
the smaller, deeper CDF-S + E-CDFS surveys and with {\it Chandra}-COSMOS,
illustrating the benefit of wide-area surveys in locating high luminosity AGN.
We also investigate the differences and similarities of X-ray and optical
selection to uncover obscured AGN in the local Universe. Finally, we estimate
the population of AGN we expect to find with increased coverage of 100 deg$^2$
or 300 deg$^2$, which will provide unprecedented insight into the high
redshift, high luminosity regime of black hole growth currently
under-represented in X-ray surveys.
We present the first results of a wide area X-ray survey within the Sloan
Digital Sky Survey (SDSS) Stripe 82, a 300 deg$^2$ region of the sky with a
substantial investment in multi-wavelength coverage. We analyzed archival {\it
Chandra} observations that cover 7.5 deg$^2$ within Stripe 82 ("Stripe 82
ACX"), reaching 4.5$\sigma$ flux limits of 7.9$\times10^{-16}$,
3.4$\times10^{-15}$ and 1.8$\times10^{-15}$ erg s$^{-1}$ cm$^{-2}$ in the soft
(0.5-2 keV), hard (2-7 keV) and full (0.5-7 keV) bands, to find 774, 239 and
1118 X-ray sources, respectively. Three hundred twenty-one sources are detected
only in the full band and 9 sources are detected solely in the soft band.
Utilizing data products from the {\it Chandra} Source Catalog, we construct
independent Log$N$-Log$S$ relationships, detailing the number density of X-ray
sources as a function of flux, which show general agreement with previous {\it
Chandra} surveys. We compare the luminosity distribution of Stripe 82 ACX with
the smaller, deeper CDF-S + E-CDFS surveys and with {\it Chandra}-COSMOS,
illustrating the benefit of wide-area surveys in locating high luminosity AGN.
We also investigate the differences and similarities of X-ray and optical
selection to uncover obscured AGN in the local Universe. Finally, we estimate
the population of AGN we expect to find with increased coverage of 100 deg$^2$
or 300 deg$^2$, which will provide unprecedented insight into the high
redshift, high luminosity regime of black hole growth currently
under-represented in X-ray surveys.
Dark matter and cosmic structure. (arXiv:1210.0544v1 [astro-ph.CO])
Dark matter and cosmic structure. (arXiv:1210.0544v1 [astro-ph.CO]):
We review the current standard model for the evolution of cosmic structure,
tracing its development over the last forty years and focusing specifically on
the role played by numerical simulations and on aspects related to the nature
of dark matter.
We review the current standard model for the evolution of cosmic structure,
tracing its development over the last forty years and focusing specifically on
the role played by numerical simulations and on aspects related to the nature
of dark matter.
Tuesday, October 2, 2012
An X-ray Detected Group of Quiescent Early-type Galaxies at z=1.6 in the Chandra Deep Field South. (arXiv:1210.0302v1 [astro-ph.CO])
An X-ray Detected Group of Quiescent Early-type Galaxies at z=1.6 in the Chandra Deep Field South. (arXiv:1210.0302v1 [astro-ph.CO]):
(Abridged) We report the discovery of an X-ray group of galaxies located at a
high redshift of z=1.61 in the Chandra Deep Field South. The group is first
identified as an extended X-ray source. We use a wealth of deep
multi-wavelength data to identify the optical counterpart -- our red sequence
finder detects a significant over-density of galaxies at z~1.6 and the
brightest group galaxy is spectroscopically confirmed at z=1.61. We measure an
X-ray luminosity of L_{0.1-2.4 keV}= 1.8\pm0.6 \times 10^{43} erg/s, which then
translates into a group mass of 3.2\pm0.8 \times 10^{13} M_sun. This is the
lowest mass group ever confirmed at z>1.5. The deep optical-nearIR images from
CANDELS reveal that the group exhibits a surprisingly prominent red sequence. A
detailed analysis of the spectral energy distributions of the group member
candidates confirms that most of them are indeed passive galaxies. Furthermore,
their structural parameters measured from the near-IR CANDELS images show that
they are morphologically early-type. The newly identified group at z=1.61 is
dominated by quiescent early-type galaxies and the group appears similar to
those in the local Universe. One possible difference is the high fraction of
AGN (38^{+23}_{-20}%), which might indicate a role for AGN in quenching. But, a
statistical sample of high-z groups is needed to draw a general picture of
groups at this redshift. Such a sample will hopefully be available in near
future surveys.
(Abridged) We report the discovery of an X-ray group of galaxies located at a
high redshift of z=1.61 in the Chandra Deep Field South. The group is first
identified as an extended X-ray source. We use a wealth of deep
multi-wavelength data to identify the optical counterpart -- our red sequence
finder detects a significant over-density of galaxies at z~1.6 and the
brightest group galaxy is spectroscopically confirmed at z=1.61. We measure an
X-ray luminosity of L_{0.1-2.4 keV}= 1.8\pm0.6 \times 10^{43} erg/s, which then
translates into a group mass of 3.2\pm0.8 \times 10^{13} M_sun. This is the
lowest mass group ever confirmed at z>1.5. The deep optical-nearIR images from
CANDELS reveal that the group exhibits a surprisingly prominent red sequence. A
detailed analysis of the spectral energy distributions of the group member
candidates confirms that most of them are indeed passive galaxies. Furthermore,
their structural parameters measured from the near-IR CANDELS images show that
they are morphologically early-type. The newly identified group at z=1.61 is
dominated by quiescent early-type galaxies and the group appears similar to
those in the local Universe. One possible difference is the high fraction of
AGN (38^{+23}_{-20}%), which might indicate a role for AGN in quenching. But, a
statistical sample of high-z groups is needed to draw a general picture of
groups at this redshift. Such a sample will hopefully be available in near
future surveys.
Hot accretion flow in black hole binaries: a link connecting X-rays to the infrared. (arXiv:1210.0236v1 [astro-ph.HE])
Hot accretion flow in black hole binaries: a link connecting X-rays to the infrared. (arXiv:1210.0236v1 [astro-ph.HE]):
Multiwavelength observations of Galactic black hole transients have opened a
new path to understanding the physics of the innermost parts of the accretion
flows. While the processes giving rise to their X-ray continuum have been
studied extensively, the emission in the optical and infrared (OIR) energy
bands was less investigated and remains poorly understood. The standard
accretion disc, which may contribute to the flux at these wavelengths, is not
capable of explaining a number of observables: the infrared excesses, fast OIR
variability and a complicated correlation with the X-rays. It was suggested
that these energy bands are dominated by the jet emission, however, this
scenario does not work in a number of cases. We suggest here an alternative,
namely that most of the OIR emission is produced by the extended hot accretion
flow. In this scenario, the OIR bands are dominated by the synchrotron
radiation from the non-thermal electrons. An additional contribution is
expected from the outer irradiated part of the accretion disc heated by the
X-rays. We discuss properties of the model and compare them to the data. We
show that the hot flow scenario is consistent with many of the observed
spectral data, at the same time naturally explaining X-ray timing properties,
fast OIR variability and its correlations with the X-rays, which were not
possible to understand within the jet paradigm.
Multiwavelength observations of Galactic black hole transients have opened a
new path to understanding the physics of the innermost parts of the accretion
flows. While the processes giving rise to their X-ray continuum have been
studied extensively, the emission in the optical and infrared (OIR) energy
bands was less investigated and remains poorly understood. The standard
accretion disc, which may contribute to the flux at these wavelengths, is not
capable of explaining a number of observables: the infrared excesses, fast OIR
variability and a complicated correlation with the X-rays. It was suggested
that these energy bands are dominated by the jet emission, however, this
scenario does not work in a number of cases. We suggest here an alternative,
namely that most of the OIR emission is produced by the extended hot accretion
flow. In this scenario, the OIR bands are dominated by the synchrotron
radiation from the non-thermal electrons. An additional contribution is
expected from the outer irradiated part of the accretion disc heated by the
X-rays. We discuss properties of the model and compare them to the data. We
show that the hot flow scenario is consistent with many of the observed
spectral data, at the same time naturally explaining X-ray timing properties,
fast OIR variability and its correlations with the X-rays, which were not
possible to understand within the jet paradigm.
3D Simulations of the Thermal X-ray Emission from Young Supernova Remnants Including Efficient Particle Acceleration. (arXiv:1210.0085v1 [astro-ph.HE])
3D Simulations of the Thermal X-ray Emission from Young Supernova Remnants Including Efficient Particle Acceleration. (arXiv:1210.0085v1 [astro-ph.HE]):
Supernova remnants (SNRs) are believed to be the major contributors to
Galactic cosmic rays. The detection of non-thermal emission from SNRs
demonstrates the presence of energetic particles, but direct signatures of
protons and other ions remain elusive. If these particles receive a sizeable
fraction of the explosion energy, the morphological and spectral evolution of
the SNR must be modified. To assess this, we run 3D hydrodynamic simulations of
a remnant coupled with a non-linear acceleration model. We obtain the
time-dependent evolution of the shocked structure, impacted by the
Rayleigh-Taylor hydrodynamic instabilities at the contact discontinuity and by
the back-reaction of particles at the forward shock. We then compute the
progressive temperature equilibration and non-equilibrium ionization state of
the plasma, and its thermal emission in each cell. This allows us to produce
the first realistic synthetic maps of the projected X-ray emission from the
SNR. Plasma conditions (temperature, ionization age) can vary widely over the
projected surface of the SNR, especially between the ejecta and the ambient
medium owing to their different composition. This demonstrates the need for
spatially-resolved spectroscopy. We find that the integrated emission is
reduced with particle back-reaction, with the effect being more significant for
the highest photon energies. Therefore different energy bands, corresponding to
different emitting elements, probe different levels of the impact of particle
acceleration. Our work provides a framework for the interpretation of SNR
observations with current X-ray missions (Chandra, XMM-Newton, Suzaku) and with
upcoming X-ray missions (such as Astro-H).
Supernova remnants (SNRs) are believed to be the major contributors to
Galactic cosmic rays. The detection of non-thermal emission from SNRs
demonstrates the presence of energetic particles, but direct signatures of
protons and other ions remain elusive. If these particles receive a sizeable
fraction of the explosion energy, the morphological and spectral evolution of
the SNR must be modified. To assess this, we run 3D hydrodynamic simulations of
a remnant coupled with a non-linear acceleration model. We obtain the
time-dependent evolution of the shocked structure, impacted by the
Rayleigh-Taylor hydrodynamic instabilities at the contact discontinuity and by
the back-reaction of particles at the forward shock. We then compute the
progressive temperature equilibration and non-equilibrium ionization state of
the plasma, and its thermal emission in each cell. This allows us to produce
the first realistic synthetic maps of the projected X-ray emission from the
SNR. Plasma conditions (temperature, ionization age) can vary widely over the
projected surface of the SNR, especially between the ejecta and the ambient
medium owing to their different composition. This demonstrates the need for
spatially-resolved spectroscopy. We find that the integrated emission is
reduced with particle back-reaction, with the effect being more significant for
the highest photon energies. Therefore different energy bands, corresponding to
different emitting elements, probe different levels of the impact of particle
acceleration. Our work provides a framework for the interpretation of SNR
observations with current X-ray missions (Chandra, XMM-Newton, Suzaku) and with
upcoming X-ray missions (such as Astro-H).
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