The origin of blue-shifted absorption features in the X-ray spectrum of PG 1211+143: Outflow or disc?. (arXiv:1306.3404v1 [astro-ph.HE]):
In some radio-quiet active galaxies (AGN), high-energy absorption features in
the x-ray spectra have been interpreted as Ultrafast Outflows (UFOs) -- highly
ionised material (e.g. Fe XXV and Fe XXVI) ejected at mildly relativistic
velocities. In some cases, these outflows can carry energy in excess of the
binding energy of the host galaxy. Needless to say, these features demand our
attention as they are strong signatures of AGN feedback and will influence
galaxy evolution. For the same reason, alternative models need to be discussed
and refuted or confirmed. Gallo & Fabian proposed that some of these features
could arise from resonance absorption of the reflected spectrum in a layer of
ionised material located above and corotating with the accretion disc.
Therefore, the absorbing medium would be subjected to similar blurring effects
as seen in the disc. A priori, the existence of such plasma above the disc is
as plausible as a fast wind. In this work, we highlight the ambiguity by
demonstrating that the absorption model can describe the ~7.6 keV absorption
feature (and possibly other features) in the quasar PG 1211+143, an AGN that is
often described as a classic example of an UFO. In this model, the 2-10 keV
spectrum would be largely reflection dominated (as opposed to power law
dominated in the wind models) and the resonance absorption would be originating
in a layer between about 6 and 60 gravitational radii. The studies of such
features constitutes a cornerstone for future X-ray observatories like Astro-H
and Athena+. Should our model prove correct, or at least important in some
cases, then absorption will provide another diagnostic tool with which to probe
the inner accretion flow with future missions.
Tuesday, June 18, 2013
On the Statistical Analysis of X-ray Polarization Measurements. (arXiv:1306.3885v1 [astro-ph.IM])
On the Statistical Analysis of X-ray Polarization Measurements. (arXiv:1306.3885v1 [astro-ph.IM]):
In many polarimetry applications, including observations in the X-ray band,
the measurement of a polarization signal can be reduced to the detection and
quantification of a deviation from uniformity of a distribution of measured
angles. We explore the statistics of such polarization measurements using Monte
Carlo simulations and chi-squared fitting methods. We compare our results to
those derived using the traditional probability density used to characterize
polarization measurements and quantify how they deviate as the intrinsic
modulation amplitude grows. We derive relations for the number of counts
required to reach a given detection level (parameterized by beta, the "number
of sigma's" of the measurement) appropriate for measuring the modulation
amplitude by itself (single interesting parameter case) or jointly with the
position angle (two interesting parameters case). We show that for the former
case when the intrinsic amplitude is equal to the well known minimum detectable
polarization (MDP) it is, on average, detected at the 3-sigma level. For the
latter case, when one requires a joint measurement at the same confidence
level, then more counts are needed than that required to achieve the MDP level.
This additional factor is amplitude-dependent, but is approximately 2.2 for
intrinsic amplitudes less than about 20%. It decreases slowly with amplitude
and is 1.8 when the amplitude is 50%. We find that the position angle
uncertainty at 1-sigma confidence is well described by the relation 28.5 (deg)
/ beta.
In many polarimetry applications, including observations in the X-ray band,
the measurement of a polarization signal can be reduced to the detection and
quantification of a deviation from uniformity of a distribution of measured
angles. We explore the statistics of such polarization measurements using Monte
Carlo simulations and chi-squared fitting methods. We compare our results to
those derived using the traditional probability density used to characterize
polarization measurements and quantify how they deviate as the intrinsic
modulation amplitude grows. We derive relations for the number of counts
required to reach a given detection level (parameterized by beta, the "number
of sigma's" of the measurement) appropriate for measuring the modulation
amplitude by itself (single interesting parameter case) or jointly with the
position angle (two interesting parameters case). We show that for the former
case when the intrinsic amplitude is equal to the well known minimum detectable
polarization (MDP) it is, on average, detected at the 3-sigma level. For the
latter case, when one requires a joint measurement at the same confidence
level, then more counts are needed than that required to achieve the MDP level.
This additional factor is amplitude-dependent, but is approximately 2.2 for
intrinsic amplitudes less than about 20%. It decreases slowly with amplitude
and is 1.8 when the amplitude is 50%. We find that the position angle
uncertainty at 1-sigma confidence is well described by the relation 28.5 (deg)
/ beta.
GRB 130606A as a Probe of the Intergalactic Medium and the Interstellar Medium in a Star-forming Galaxy in the First Gyr After the Big Bang. (arXiv:1306.3949v1 [astro-ph.CO])
GRB 130606A as a Probe of the Intergalactic Medium and the Interstellar Medium in a Star-forming Galaxy in the First Gyr After the Big Bang. (arXiv:1306.3949v1 [astro-ph.CO]):
We present high signal-to-noise ratio Gemini and MMT spectroscopy of the
optical afterglow of the gamma-ray burst (GRB) 130606A at redshift z=5.913,
discovered by Swift. This is the first high-redshift GRB afterglow to have
spectra of comparable quality to those of z~6 quasars. The data exhibit a
smooth continuum at near-infrared wavelengths that is sharply cut off blueward
of 8410 Angs due to absorption from Ly-alpha at redshift z~5.91, with some flux
transmitted through the Ly-alpha forest between 7000-7800 Angs. We use column
densities inferred from metal absorption lines to constrain the metallicity of
the host galaxy between a lower limit of [Si/H]>-1.7 and an upper limit of
[S/H]<-0.5 set by the non-detection of S II absorption. We demonstrate
consistency between the dramatic evolution in the transmission fraction of
Ly-alpha seen in this spectrum over the redshift range z=4.9 to 5.85 with that
previously measured from observations of high-redshift quasars. There is an
extended redshift interval of Delta-z=0.12 in the Ly-alpha forest at z=5.77
with no detected transmission, leading to a 3-sigma upper limit on the mean
Ly-alpha transmission fraction of <0.2% (or tau_eff(Ly-alpha) > 6.4). This is
comparable to the lowest-redshift Gunn-Peterson troughs found in quasar
spectra. Some Ly-beta and Ly-gamma transmission is detected in this redshift
window, indicating that it is not completely opaque, and hence that the IGM is
nonetheless mostly ionized at these redshifts. GRB 130606A thus for the first
time realizes the promise of GRBs as probes of the first galaxies and cosmic
reionization.
We present high signal-to-noise ratio Gemini and MMT spectroscopy of the
optical afterglow of the gamma-ray burst (GRB) 130606A at redshift z=5.913,
discovered by Swift. This is the first high-redshift GRB afterglow to have
spectra of comparable quality to those of z~6 quasars. The data exhibit a
smooth continuum at near-infrared wavelengths that is sharply cut off blueward
of 8410 Angs due to absorption from Ly-alpha at redshift z~5.91, with some flux
transmitted through the Ly-alpha forest between 7000-7800 Angs. We use column
densities inferred from metal absorption lines to constrain the metallicity of
the host galaxy between a lower limit of [Si/H]>-1.7 and an upper limit of
[S/H]<-0.5 set by the non-detection of S II absorption. We demonstrate
consistency between the dramatic evolution in the transmission fraction of
Ly-alpha seen in this spectrum over the redshift range z=4.9 to 5.85 with that
previously measured from observations of high-redshift quasars. There is an
extended redshift interval of Delta-z=0.12 in the Ly-alpha forest at z=5.77
with no detected transmission, leading to a 3-sigma upper limit on the mean
Ly-alpha transmission fraction of <0.2% (or tau_eff(Ly-alpha) > 6.4). This is
comparable to the lowest-redshift Gunn-Peterson troughs found in quasar
spectra. Some Ly-beta and Ly-gamma transmission is detected in this redshift
window, indicating that it is not completely opaque, and hence that the IGM is
nonetheless mostly ionized at these redshifts. GRB 130606A thus for the first
time realizes the promise of GRBs as probes of the first galaxies and cosmic
reionization.
Sunday, June 16, 2013
CXOU J005047.9-731817: a 292-s X-ray binary pulsar in the Small Magellanic Cloud. (arXiv:1306.1106v1 [astro-ph.HE])
CXOU J005047.9-731817: a 292-s X-ray binary pulsar in the Small Magellanic Cloud. (arXiv:1306.1106v1 [astro-ph.HE]):
We report on the discovery of a transient X-ray pulsars, located in the Small
Magellanic Cloud, with a pulse period of 292 s. A series of Chandra pointings
fortuitously recorded in 2010 April-May the occurrence of a two-weeks-long
outburst, during which the source luminosity increased by a factor of about
100, reaching a peak of ~1E36 erg/s (for a distance of 61 kpc). Complex-shape
and energy-dependent pulsations were detected close to the outburst peak and
during the very first part of its decay phase. During the outburst, the
phase-averaged spectrum of the pulsar was well described by an absorbed power
law with photon index ~0.6, but large variations as a function of phase were
present. The source was also detected by Chandra several times (during 2002,
2003, 2006, and 2010) at a quiescent level of ~1E34 erg/s. In 2012 we performed
an infrared photometric follow-up of the R ~ 15 mag optical counterpart with
the ESO/VLT and a spectroscopic observation by means of the CTIO telescope. The
optical spectra suggest a late-Oe or early-Be V-III luminosity-class star,
though a more evolved companion cannot be ruled out by our data (we can exclude
a luminosity class I and a spectral type later than B2). Finally, we show that
the outburst main parameters (duration and peak luminosity) can be accounted
for by interpreting the source transient activity as a type I outburst in a Be
X-ray binary.
We report on the discovery of a transient X-ray pulsars, located in the Small
Magellanic Cloud, with a pulse period of 292 s. A series of Chandra pointings
fortuitously recorded in 2010 April-May the occurrence of a two-weeks-long
outburst, during which the source luminosity increased by a factor of about
100, reaching a peak of ~1E36 erg/s (for a distance of 61 kpc). Complex-shape
and energy-dependent pulsations were detected close to the outburst peak and
during the very first part of its decay phase. During the outburst, the
phase-averaged spectrum of the pulsar was well described by an absorbed power
law with photon index ~0.6, but large variations as a function of phase were
present. The source was also detected by Chandra several times (during 2002,
2003, 2006, and 2010) at a quiescent level of ~1E34 erg/s. In 2012 we performed
an infrared photometric follow-up of the R ~ 15 mag optical counterpart with
the ESO/VLT and a spectroscopic observation by means of the CTIO telescope. The
optical spectra suggest a late-Oe or early-Be V-III luminosity-class star,
though a more evolved companion cannot be ruled out by our data (we can exclude
a luminosity class I and a spectral type later than B2). Finally, we show that
the outburst main parameters (duration and peak luminosity) can be accounted
for by interpreting the source transient activity as a type I outburst in a Be
X-ray binary.
What can the spatial distribution of galaxy clusters tell about their scaling relations?. (arXiv:1306.1399v1 [astro-ph.CO])
What can the spatial distribution of galaxy clusters tell about their scaling relations?. (arXiv:1306.1399v1 [astro-ph.CO]):
We aim to quantify the capability of the inhomogeneous distribution of galaxy
clusters, represented by the two-point statistics in Fourier space, to retrieve
information on the underlying scaling relations. As an example, we use the
mass-X ray luminosity of galaxy clusters. We define the luminosity-weighted
power spectrum and introduce the luminosity power spectrum as a direct
assessment of the clustering of X-ray luminosity. Using a suite of halo
catalogs extracted from $N$-body simulations and realistic estimates of the
mass-X ray luminosity relation, we measure the luminosity-weighted and the
luminosity power spectrum of galaxy clusters. By means of a Fisher matrix
analysis, we quantify the content of information (by means of a Figure-of
Merit) encoded in the amplitude, shape and full-shape of these probes. The full
shape of the luminosity power spectrum, when analyzed up to scales of $k~0.2 h/
Mpc$, yields a figure of merit which is only one order of magnitude below the
value encoded in X-ray luminosity function estimated from the same sample. This
is a significant improvement with respect to the FoM obtained from the
estimates of the unweighted power spectrum. We therefore suggest future
clustering analysis of galaxy clusters to take advantage of the luminosity
power spectrum when aiming at simultaneously constraining cosmological and
astrophysical parameters (Abridged)
We aim to quantify the capability of the inhomogeneous distribution of galaxy
clusters, represented by the two-point statistics in Fourier space, to retrieve
information on the underlying scaling relations. As an example, we use the
mass-X ray luminosity of galaxy clusters. We define the luminosity-weighted
power spectrum and introduce the luminosity power spectrum as a direct
assessment of the clustering of X-ray luminosity. Using a suite of halo
catalogs extracted from $N$-body simulations and realistic estimates of the
mass-X ray luminosity relation, we measure the luminosity-weighted and the
luminosity power spectrum of galaxy clusters. By means of a Fisher matrix
analysis, we quantify the content of information (by means of a Figure-of
Merit) encoded in the amplitude, shape and full-shape of these probes. The full
shape of the luminosity power spectrum, when analyzed up to scales of $k~0.2 h/
Mpc$, yields a figure of merit which is only one order of magnitude below the
value encoded in X-ray luminosity function estimated from the same sample. This
is a significant improvement with respect to the FoM obtained from the
estimates of the unweighted power spectrum. We therefore suggest future
clustering analysis of galaxy clusters to take advantage of the luminosity
power spectrum when aiming at simultaneously constraining cosmological and
astrophysical parameters (Abridged)
Constraints on porosity and mass loss in O-star winds from modeling of X-ray emission line profile shapes. (arXiv:1305.5595v1 [astro-ph.SR])
Constraints on porosity and mass loss in O-star winds from modeling of X-ray emission line profile shapes. (arXiv:1305.5595v1 [astro-ph.SR]):
We fit X-ray emission line profiles in high resolution XMM-Newton and Chandra
grating spectra of the early O supergiant Zeta Pup with models that include the
effects of porosity in the stellar wind. We explore the effects of porosity due
to both spherical and flattened clumps. We find that porosity models with
flattened clumps oriented parallel to the photosphere provide poor fits to
observed line shapes. However, porosity models with isotropic clumps can
provide acceptable fits to observed line shapes, but only if the porosity
effect is moderate. We quantify the degeneracy between porosity effects from
isotropic clumps and the mass-loss rate inferred from the X-ray line shapes,
and we show that only modest increases in the mass-loss rate (<~ 40%) are
allowed if moderate porosity effects (h_infinity <~ R_*) are assumed to be
important. Large porosity lengths, and thus strong porosity effects, are ruled
out regardless of assumptions about clump shape. Thus, X-ray mass-loss rate
estimates are relatively insensitive to both optically thin and optically thick
clumping. This supports the use of X-ray spectroscopy as a mass-loss rate
calibration for bright, nearby O stars.
We fit X-ray emission line profiles in high resolution XMM-Newton and Chandra
grating spectra of the early O supergiant Zeta Pup with models that include the
effects of porosity in the stellar wind. We explore the effects of porosity due
to both spherical and flattened clumps. We find that porosity models with
flattened clumps oriented parallel to the photosphere provide poor fits to
observed line shapes. However, porosity models with isotropic clumps can
provide acceptable fits to observed line shapes, but only if the porosity
effect is moderate. We quantify the degeneracy between porosity effects from
isotropic clumps and the mass-loss rate inferred from the X-ray line shapes,
and we show that only modest increases in the mass-loss rate (<~ 40%) are
allowed if moderate porosity effects (h_infinity <~ R_*) are assumed to be
important. Large porosity lengths, and thus strong porosity effects, are ruled
out regardless of assumptions about clump shape. Thus, X-ray mass-loss rate
estimates are relatively insensitive to both optically thin and optically thick
clumping. This supports the use of X-ray spectroscopy as a mass-loss rate
calibration for bright, nearby O stars.
Obscured AGN at z~1 from the zCOSMOS-Bright Survey I. Selection and Optical Properties of a [Ne v]-selected sample. (arXiv:1305.6167v1 [astro-ph.CO])
Obscured AGN at z~1 from the zCOSMOS-Bright Survey I. Selection and Optical Properties of a [Ne v]-selected sample. (arXiv:1305.6167v1 [astro-ph.CO]):
A sample of 94 narrow line AGN with 0.65<z<1.20 has been selected from the
20k-Bright zCOSMOS galaxy sample by detection of the high-ionization [NeV]3426
line. Taking advantage of the large amount of data available in the COSMOS
field, the properties of the [NeV]-selected Type-2 AGN have been investigated,
focusing on their host galaxies, X-ray emission, and optical line flux ratios.
Finally, the diagnostic developed by Gilli et al. (2010), based on the X-ray to
[NeV] luminosity ratio, has been exploited to search for the more heavily
obscured AGN. We found that [Ne v]-selected narrow line AGN have Seyfert 2-like
optical spectra, although with emission line ratios diluted by a star-forming
component. The ACS morphologies and stellar component in the optical spectra
indicate a preference for our Type-2 AGN to be hosted in early-spirals with
stellar masses greater than 10^(9.5-10)Msun, on average higher than those of
the galaxy parent sample. The fraction of galaxies hosting [NeV]-selected
obscured AGN increases with the stellar mass, reaching a maximum of about 3% at
2x10^11 Msun. A comparison with other selection techniques at z~1 shows that
the detection of the [Ne v] line is an effective method to select AGN in the
optical band, in particular the most heavily obscured ones, but can not provide
by itself a complete census of AGN2. Finally, the high fraction of
[NeV]-selected Type-2 AGN not detected in medium-deep Chandra observations
(67%) is suggestive of the inclusion of Compton-thick sources in our sample.
The presence of a population of heavily obscured AGN is corroborated by the
X-ray to [NeV] ratio; we estimated, by mean of X-ray stacking technique and
simulations, that the Compton-thick fraction in our sample of Type-2 AGN is
43+-4%, in good agreement with standard assumptions by the XRB synthesis
models.
A sample of 94 narrow line AGN with 0.65<z<1.20 has been selected from the
20k-Bright zCOSMOS galaxy sample by detection of the high-ionization [NeV]3426
line. Taking advantage of the large amount of data available in the COSMOS
field, the properties of the [NeV]-selected Type-2 AGN have been investigated,
focusing on their host galaxies, X-ray emission, and optical line flux ratios.
Finally, the diagnostic developed by Gilli et al. (2010), based on the X-ray to
[NeV] luminosity ratio, has been exploited to search for the more heavily
obscured AGN. We found that [Ne v]-selected narrow line AGN have Seyfert 2-like
optical spectra, although with emission line ratios diluted by a star-forming
component. The ACS morphologies and stellar component in the optical spectra
indicate a preference for our Type-2 AGN to be hosted in early-spirals with
stellar masses greater than 10^(9.5-10)Msun, on average higher than those of
the galaxy parent sample. The fraction of galaxies hosting [NeV]-selected
obscured AGN increases with the stellar mass, reaching a maximum of about 3% at
2x10^11 Msun. A comparison with other selection techniques at z~1 shows that
the detection of the [Ne v] line is an effective method to select AGN in the
optical band, in particular the most heavily obscured ones, but can not provide
by itself a complete census of AGN2. Finally, the high fraction of
[NeV]-selected Type-2 AGN not detected in medium-deep Chandra observations
(67%) is suggestive of the inclusion of Compton-thick sources in our sample.
The presence of a population of heavily obscured AGN is corroborated by the
X-ray to [NeV] ratio; we estimated, by mean of X-ray stacking technique and
simulations, that the Compton-thick fraction in our sample of Type-2 AGN is
43+-4%, in good agreement with standard assumptions by the XRB synthesis
models.
Energy Feedback from X-ray Binaries in the Early Universe. (arXiv:1306.1405v1 [astro-ph.CO])
Energy Feedback from X-ray Binaries in the Early Universe. (arXiv:1306.1405v1 [astro-ph.CO]):
X-ray photons, because of their long mean-free paths, can easily escape the
galactic environments where they are produced, and interact at long distances
with the inter-galactic medium, potentially having a significant contribution
to the heating and reionization of the early Universe. The two most important
sources of X-ray photons in the Universe are active galactic nuclei (AGN) and
X-ray binaries (XRBs). In this Letter we use results from detailed, large scale
population synthesis simulations to study the energy feedback of XRBs, from the
first galaxies (z~20) until today. We estimate that X-ray emission from XRBs
dominates over AGN at z>6-8. The shape of the spectral energy distribution of
the emission from XRBs shows no changes with redshift, in contrast to its
normalization which evolves by ~4 orders of magnitude, primarily due to the
evolution of the cosmic star-formation rate. However, the metallicity and the
mean stellar age of a given XRB population affect significantly its X-ray
output. Specifically, the X-ray luminosity from high-mass XRBs per unit of
star-formation rate varies by more than an order of magnitude going from solar
metallicity to less than 10% solar, and the X-ray luminosity from low-mass XRBs
per unit of stellar mass peaks at an age of ~300 Myr and then decreases
gradually at later times, showing little variation for mean stellar ages >3
Gyr. Finally, we provide analytical and tabulated prescriptions for the energy
output of XRBs, that can be directly incorporated in cosmological simulations.
X-ray photons, because of their long mean-free paths, can easily escape the
galactic environments where they are produced, and interact at long distances
with the inter-galactic medium, potentially having a significant contribution
to the heating and reionization of the early Universe. The two most important
sources of X-ray photons in the Universe are active galactic nuclei (AGN) and
X-ray binaries (XRBs). In this Letter we use results from detailed, large scale
population synthesis simulations to study the energy feedback of XRBs, from the
first galaxies (z~20) until today. We estimate that X-ray emission from XRBs
dominates over AGN at z>6-8. The shape of the spectral energy distribution of
the emission from XRBs shows no changes with redshift, in contrast to its
normalization which evolves by ~4 orders of magnitude, primarily due to the
evolution of the cosmic star-formation rate. However, the metallicity and the
mean stellar age of a given XRB population affect significantly its X-ray
output. Specifically, the X-ray luminosity from high-mass XRBs per unit of
star-formation rate varies by more than an order of magnitude going from solar
metallicity to less than 10% solar, and the X-ray luminosity from low-mass XRBs
per unit of stellar mass peaks at an age of ~300 Myr and then decreases
gradually at later times, showing little variation for mean stellar ages >3
Gyr. Finally, we provide analytical and tabulated prescriptions for the energy
output of XRBs, that can be directly incorporated in cosmological simulations.
Wednesday, June 12, 2013
On the Virialization of Disk Winds: Implications for the Black Hole Mass Estimates in AGN. (arXiv:1306.1090v1 [astro-ph.GA])
On the Virialization of Disk Winds: Implications for the Black Hole Mass Estimates in AGN. (arXiv:1306.1090v1 [astro-ph.GA]):
[abbreviated] Estimating the mass of a supermassive black hole (SMBH) in an
active galactic nucleus (AGN) usually relies on the assumption that the broad
line region (BLR) is virialized. However, this assumption seems invalid in BLR
models that consists of an accretion disk and its wind. The disk is likely
Keplerian and therefore virialized. However, the wind material must, beyond a
certain point, be dominated by an outward force that is stronger than gravity.
Here, we analyze hydrodynamic simulations of four different disk winds: an
isothermal wind, a thermal wind from an X-ray heated disk, and two line-driven
winds, one with and the other without X-ray heating and cooling. For each
model, we check whether gravity governs the flow properties, by computing and
analyzing the volume-integrated quantities that appear in the virial theorem:
internal, kinetic, and gravitational energies, We find that in the first two
models, the winds are non-virialized whereas the two line-driven disk winds are
virialized up to a relatively large distance. The line-driven winds are
virialized because they accelerate slowly so that the rotational velocity is
dominant and the wind base is very dense. For the two virialized winds, the
so-called projected virial factor scales with inclination angle as 1/
\sin^2{i}. Finally, we demonstrate that an outflow from a Keplerian disk
becomes unvirialized more slowly when it conserves the gas specific angular
momentum -- as in the models considered here, than when it conserves the
angular velocity -- as in the so-called magneto-centrifugal winds.
[abbreviated] Estimating the mass of a supermassive black hole (SMBH) in an
active galactic nucleus (AGN) usually relies on the assumption that the broad
line region (BLR) is virialized. However, this assumption seems invalid in BLR
models that consists of an accretion disk and its wind. The disk is likely
Keplerian and therefore virialized. However, the wind material must, beyond a
certain point, be dominated by an outward force that is stronger than gravity.
Here, we analyze hydrodynamic simulations of four different disk winds: an
isothermal wind, a thermal wind from an X-ray heated disk, and two line-driven
winds, one with and the other without X-ray heating and cooling. For each
model, we check whether gravity governs the flow properties, by computing and
analyzing the volume-integrated quantities that appear in the virial theorem:
internal, kinetic, and gravitational energies, We find that in the first two
models, the winds are non-virialized whereas the two line-driven disk winds are
virialized up to a relatively large distance. The line-driven winds are
virialized because they accelerate slowly so that the rotational velocity is
dominant and the wind base is very dense. For the two virialized winds, the
so-called projected virial factor scales with inclination angle as 1/
\sin^2{i}. Finally, we demonstrate that an outflow from a Keplerian disk
becomes unvirialized more slowly when it conserves the gas specific angular
momentum -- as in the models considered here, than when it conserves the
angular velocity -- as in the so-called magneto-centrifugal winds.
SZ observations with AMI of the hottest galaxy clusters detected in the XMM-Newton Cluster Survey. (arXiv:1305.6654v1 [astro-ph.CO])
SZ observations with AMI of the hottest galaxy clusters detected in the XMM-Newton Cluster Survey. (arXiv:1305.6654v1 [astro-ph.CO]):
We have obtained deep SZ observations towards 15 of the apparently hottest
XMM Cluster Survey (XCS) clusters that can be observed with the Arcminute
Microkelvin Imager (AMI). We use a Bayesian analysis to quantify the
significance of our SZ detections. We detect the SZ effect at high significance
towards three of the clusters and at lower significance for a further two
clusters. Towards the remaining ten clusters, no clear SZ signal was measured.
We derive cluster parameters using the XCS mass estimates as a prior in our
Bayesian analysis. For all AMI-detected clusters, we calculate large-scale mass
and temperature estimates while for all undetected clusters we determine upper
limits on these parameters. We find that the large- scale mean temperatures
derived from our AMI SZ measurements (and the upper limits from null
detections) are substantially lower than the XCS-based core-temperature
estimates. For clusters detected in the SZ, the mean temperature is, on
average, a factor of 1.4 lower than temperatures from the XCS. For clusters
undetected in SZ, the average 68% upper limit on the mean temperature is a
factor of 1.9 below the XCS temperature.
We have obtained deep SZ observations towards 15 of the apparently hottest
XMM Cluster Survey (XCS) clusters that can be observed with the Arcminute
Microkelvin Imager (AMI). We use a Bayesian analysis to quantify the
significance of our SZ detections. We detect the SZ effect at high significance
towards three of the clusters and at lower significance for a further two
clusters. Towards the remaining ten clusters, no clear SZ signal was measured.
We derive cluster parameters using the XCS mass estimates as a prior in our
Bayesian analysis. For all AMI-detected clusters, we calculate large-scale mass
and temperature estimates while for all undetected clusters we determine upper
limits on these parameters. We find that the large- scale mean temperatures
derived from our AMI SZ measurements (and the upper limits from null
detections) are substantially lower than the XCS-based core-temperature
estimates. For clusters detected in the SZ, the mean temperature is, on
average, a factor of 1.4 lower than temperatures from the XCS. For clusters
undetected in SZ, the average 68% upper limit on the mean temperature is a
factor of 1.9 below the XCS temperature.
Innermost structure and near-infrared radiation of dusty clumpy tori in active galactic nuclei. (arXiv:1306.0188v1 [astro-ph.HE])
Innermost structure and near-infrared radiation of dusty clumpy tori in active galactic nuclei. (arXiv:1306.0188v1 [astro-ph.HE]):
The dusty clumpy torus surrounds the central black hole (BH) and the
accretion disk in active galactic nuclei, and governs the growth of
super-massive BHs via gas fueling towards the central engine. Near-infrared
(NIR) monitoring observations have revealed that the torus inner radius is
determined by the dust sublimation process. However, the observed radii are
systematically smaller than the theoretical predictions by a factor of three.
We take into account the anisotropic illumination by the central accretion
disk to the torus, and calculate the innermost structure of the torus and the
NIR time variablity. We then show that the anisotropy naturally solves the
systematic descrepancy and that the viewing angle is the primary source to
produce an object-to-object scatter of the NIR time delay. Dynamics of clumps
at the innermost region of the torus will be unveiled via future
high-resolution X-ray spectroscopy (e.g., Astro-H).
The dusty clumpy torus surrounds the central black hole (BH) and the
accretion disk in active galactic nuclei, and governs the growth of
super-massive BHs via gas fueling towards the central engine. Near-infrared
(NIR) monitoring observations have revealed that the torus inner radius is
determined by the dust sublimation process. However, the observed radii are
systematically smaller than the theoretical predictions by a factor of three.
We take into account the anisotropic illumination by the central accretion
disk to the torus, and calculate the innermost structure of the torus and the
NIR time variablity. We then show that the anisotropy naturally solves the
systematic descrepancy and that the viewing angle is the primary source to
produce an object-to-object scatter of the NIR time delay. Dynamics of clumps
at the innermost region of the torus will be unveiled via future
high-resolution X-ray spectroscopy (e.g., Astro-H).
Inverse Compton X-ray signature of AGN feedback. (arXiv:1306.2636v1 [astro-ph.GA])
Inverse Compton X-ray signature of AGN feedback. (arXiv:1306.2636v1 [astro-ph.GA]):
Bright AGN frequently show ultra-fast outflows (UFOs) with outflow velocities
vout ! 0.1c. These outflows may be the source of AGN feedback on their host
galaxies sought by galaxy formation modellers. The exact effect of the outflows
on the ambient galaxy gas strongly depends on whether the shocked UFOs cool
rapidly or not. This in turn depends on whether the shocked electrons share the
same temperature as ions (one temperature regime; 1T) or decouple (2T), as has
been recently suggested. Here we calculate the Inverse Compton spectrum emitted
by such shocks, finding a broad feature potentially detectable either in
mid-to-high energy X-rays (1T case) or only in the soft X-rays (2T). We argue
that current observations of AGN do not seem to show evidence for the 1T
component, while the limits on the 2T emission are far weaker. This suggests
that UFOs are in the energy-driven regime outside the central few pc, and must
pump considerable amounts of not only momentum but also energy into the ambient
gas. We encourage X-ray observers to look for the Inverse Compton components
calculated here in order to constrain AGN feedback models further.
Bright AGN frequently show ultra-fast outflows (UFOs) with outflow velocities
vout ! 0.1c. These outflows may be the source of AGN feedback on their host
galaxies sought by galaxy formation modellers. The exact effect of the outflows
on the ambient galaxy gas strongly depends on whether the shocked UFOs cool
rapidly or not. This in turn depends on whether the shocked electrons share the
same temperature as ions (one temperature regime; 1T) or decouple (2T), as has
been recently suggested. Here we calculate the Inverse Compton spectrum emitted
by such shocks, finding a broad feature potentially detectable either in
mid-to-high energy X-rays (1T case) or only in the soft X-rays (2T). We argue
that current observations of AGN do not seem to show evidence for the 1T
component, while the limits on the 2T emission are far weaker. This suggests
that UFOs are in the energy-driven regime outside the central few pc, and must
pump considerable amounts of not only momentum but also energy into the ambient
gas. We encourage X-ray observers to look for the Inverse Compton components
calculated here in order to constrain AGN feedback models further.
Broad Absorption Line Quasars with Redshifted Troughs: High-Velocity Infall or Rotationally Dominated Outflows?. (arXiv:1306.2680v1 [astro-ph.CO])
Broad Absorption Line Quasars with Redshifted Troughs: High-Velocity Infall or Rotationally Dominated Outflows?. (arXiv:1306.2680v1 [astro-ph.CO]):
We report the discovery in the Sloan Digital Sky Survey and the SDSS-III
Baryon Oscillation Spectroscopic Survey of seventeen broad absorption line
(BAL) quasars with high-ionization troughs that include absorption redshifted
relative to the quasar rest frame. The redshifted troughs extend to velocities
up to v=12,000 km/s and the trough widths exceed 3000 km/s in all but one case.
Approximately 1 in 1000 BAL quasars with blueshifted C IV absorption also has
redshifted C IV absorption; objects with C IV absorption present only at
redshifted velocities are roughly four times rarer. In more than half of our
objects, redshifted absorption is seen in C II or Al III as well as C IV,
making low-ionization absorption at least ten times more common among BAL
quasars with redshifted troughs than among standard BAL quasars. However, the C
IV absorption equivalent widths in our objects are on average smaller than
those of standard BAL quasars with low-ionization absorption. We consider
several possible ways of generating redshifted absorption. The two most likely
possibilities may be at work simultaneously, in the same objects or in
different ones. Rotationally dominated outflows seen against a quasar's
extended continuum source can produce redshifted and blueshifted absorption,
but variability consistent with this scenario is seen in only one of the four
objects with multiple spectra. The infall of relatively dense and
low-ionization gas to radii as small as 400 Schwarzschild radii can in
principle explain the observed range of trough profiles, but current models do
not easily explain the origin and survival of such gas. Whatever the origin(s)
of the absorbing gas in these objects, it must be located at small radii to
explain its large redshifted velocities, and thus offers a novel probe of the
inner regions of quasars.
We report the discovery in the Sloan Digital Sky Survey and the SDSS-III
Baryon Oscillation Spectroscopic Survey of seventeen broad absorption line
(BAL) quasars with high-ionization troughs that include absorption redshifted
relative to the quasar rest frame. The redshifted troughs extend to velocities
up to v=12,000 km/s and the trough widths exceed 3000 km/s in all but one case.
Approximately 1 in 1000 BAL quasars with blueshifted C IV absorption also has
redshifted C IV absorption; objects with C IV absorption present only at
redshifted velocities are roughly four times rarer. In more than half of our
objects, redshifted absorption is seen in C II or Al III as well as C IV,
making low-ionization absorption at least ten times more common among BAL
quasars with redshifted troughs than among standard BAL quasars. However, the C
IV absorption equivalent widths in our objects are on average smaller than
those of standard BAL quasars with low-ionization absorption. We consider
several possible ways of generating redshifted absorption. The two most likely
possibilities may be at work simultaneously, in the same objects or in
different ones. Rotationally dominated outflows seen against a quasar's
extended continuum source can produce redshifted and blueshifted absorption,
but variability consistent with this scenario is seen in only one of the four
objects with multiple spectra. The infall of relatively dense and
low-ionization gas to radii as small as 400 Schwarzschild radii can in
principle explain the observed range of trough profiles, but current models do
not easily explain the origin and survival of such gas. Whatever the origin(s)
of the absorbing gas in these objects, it must be located at small radii to
explain its large redshifted velocities, and thus offers a novel probe of the
inner regions of quasars.
Chandra Spectroscopy of MAXI J1305-704: Detection of an Infalling Black Hole Disk Wind?. (arXiv:1306.2915v1 [astro-ph.HE])
Chandra Spectroscopy of MAXI J1305-704: Detection of an Infalling Black Hole Disk Wind?. (arXiv:1306.2915v1 [astro-ph.HE]):
We report on a Chandra/HETG X-ray spectrum of the transient X-ray binary MAXI
J1305-704. A rich absorption complex is detected in the Fe L band, including
density-sensitive lines from Fe XX, XXI, and XXII. Spectral analysis over three
wavelength bands with a large grid of XSTAR photoionization models generally
requires a gas density of n > 1 E+17 cm^-3. Assuming a luminosity of L = 1 E+37
erg/s, fits to the 10-14 Angstrom band constrain the absorbing gas to lie
within r = 3.9 +/- 0.7 E+3 km from the central engine, or about r = 520 +/- 90
(M/5 Msun) r_g, where r_g = GM/c^2. At this small distance from the compact
object, gas in stable orbits should have a gravitational red-shift of z = v/c =
3 +/- 1 E-3 (M/5 Msun), and any tenuous inflowing gas should have a free-fall
velocity of v/c = 6 +/- 1 E-2 (M/5 Msun)^(1/2). The best-fit single-zone
photoionization models measure a red-shift of v/c = 2.6-3.2 E-3. Models with
two absorbing zones provide significantly improved fits, and the additional
zone is measured to have a red-shift of v/c =4.6-4.9 E-2. Thus, the observed
shifts are broadly consistent with those expected at the photoionization
radius. The absorption spectrum revealed in MAXI J1305-704 may be best
explained in terms of a "failed wind" like those predicted in some recent
numerical simulations of black hole accretion flows. The robustness of the
velocity shifts was explored through detailed simulations with the Chandra/MARX
ray-tracing package, and analysis of the zeroth-order ACIS-S3 spectrum. The
simulations and ACIS spectrum suggest that the shifts are not instrumental;
however, strong caution is warranted. We discuss our results in the context of
accretion flows in stellar-mass black holes and active galactic nuclei, and the
potential role of failed winds in emerging connections between disk outflows
and black hole state transitions.
We report on a Chandra/HETG X-ray spectrum of the transient X-ray binary MAXI
J1305-704. A rich absorption complex is detected in the Fe L band, including
density-sensitive lines from Fe XX, XXI, and XXII. Spectral analysis over three
wavelength bands with a large grid of XSTAR photoionization models generally
requires a gas density of n > 1 E+17 cm^-3. Assuming a luminosity of L = 1 E+37
erg/s, fits to the 10-14 Angstrom band constrain the absorbing gas to lie
within r = 3.9 +/- 0.7 E+3 km from the central engine, or about r = 520 +/- 90
(M/5 Msun) r_g, where r_g = GM/c^2. At this small distance from the compact
object, gas in stable orbits should have a gravitational red-shift of z = v/c =
3 +/- 1 E-3 (M/5 Msun), and any tenuous inflowing gas should have a free-fall
velocity of v/c = 6 +/- 1 E-2 (M/5 Msun)^(1/2). The best-fit single-zone
photoionization models measure a red-shift of v/c = 2.6-3.2 E-3. Models with
two absorbing zones provide significantly improved fits, and the additional
zone is measured to have a red-shift of v/c =4.6-4.9 E-2. Thus, the observed
shifts are broadly consistent with those expected at the photoionization
radius. The absorption spectrum revealed in MAXI J1305-704 may be best
explained in terms of a "failed wind" like those predicted in some recent
numerical simulations of black hole accretion flows. The robustness of the
velocity shifts was explored through detailed simulations with the Chandra/MARX
ray-tracing package, and analysis of the zeroth-order ACIS-S3 spectrum. The
simulations and ACIS spectrum suggest that the shifts are not instrumental;
however, strong caution is warranted. We discuss our results in the context of
accretion flows in stellar-mass black holes and active galactic nuclei, and the
potential role of failed winds in emerging connections between disk outflows
and black hole state transitions.
Pulse Profiles from Spinning Neutron Stars in the Hartle-Thorne Approximation. (arXiv:1305.6615v1 [astro-ph.HE])
Pulse Profiles from Spinning Neutron Stars in the Hartle-Thorne Approximation. (arXiv:1305.6615v1 [astro-ph.HE]):
We present a new numerical algorithm for the calculation of pulse profiles
from spinning neutron stars in the Hartle-Thorne approximation. Our approach
allows us to formally take into account the effects of Doppler shifts and
aberration, of frame dragging, as well as of the oblateness of the stellar
surface and of its quadrupole moment. We confirm an earlier result that
neglecting the oblateness of the neutron-star surface leads to ~5-30% errors in
the calculated profiles and further show that neglecting the quadrupole moment
of its spacetime leads to ~1-5% errors at a spin frequency of 600 Hz. We
discuss the implications of our results for the measurements of neutron-star
masses and radii with upcoming X-ray missions, such as NASA's NICER and ESA's
LOFT.
We present a new numerical algorithm for the calculation of pulse profiles
from spinning neutron stars in the Hartle-Thorne approximation. Our approach
allows us to formally take into account the effects of Doppler shifts and
aberration, of frame dragging, as well as of the oblateness of the stellar
surface and of its quadrupole moment. We confirm an earlier result that
neglecting the oblateness of the neutron-star surface leads to ~5-30% errors in
the calculated profiles and further show that neglecting the quadrupole moment
of its spacetime leads to ~1-5% errors at a spin frequency of 600 Hz. We
discuss the implications of our results for the measurements of neutron-star
masses and radii with upcoming X-ray missions, such as NASA's NICER and ESA's
LOFT.
Can we reproduce the X-ray background spectral shape using local AGN?. (arXiv:1305.6611v1 [astro-ph.HE])
Can we reproduce the X-ray background spectral shape using local AGN?. (arXiv:1305.6611v1 [astro-ph.HE]):
The X-ray background (XRB) is due to the aggregate of active galactic nuclei
(AGN), which peak in activity at z~1 and is often modeled as the sum of
different proportions of unabsorbed, moderately- and heavily-absorbed AGN. We
present the summed spectrum of a complete sample of local AGN (the Northern
Galactic Cap of the 58-month Swift/BAT catalog, z<0.2) using 0.4-200keV data
and directly determine the different proportions of unabsorbed, moderately and
heavily-absorbed AGN that make up the summed spectrum. This stacked low
redshift AGN spectrum is remarkably similar in shape to the XRB spectrum (when
shifted to z~1), but the observed proportions of different absorption
populations differ from most XRB synthesis models. AGN with Compton-thick
absorption account for only ~12% of the sample, but produce a significant
contribution to the overall spectrum. We confirm that Compton reflection is
more prominent in moderately-absorbed AGN and that the photon index differs
intrinsically between unabsorbed and absorbed AGN. The AGN in our sample
account for only ~1% of the XRB intensity. The reproduction of the XRB spectral
shape suggests that strong evolution in individual AGN properties is not
required between z~0 and 1.
The X-ray background (XRB) is due to the aggregate of active galactic nuclei
(AGN), which peak in activity at z~1 and is often modeled as the sum of
different proportions of unabsorbed, moderately- and heavily-absorbed AGN. We
present the summed spectrum of a complete sample of local AGN (the Northern
Galactic Cap of the 58-month Swift/BAT catalog, z<0.2) using 0.4-200keV data
and directly determine the different proportions of unabsorbed, moderately and
heavily-absorbed AGN that make up the summed spectrum. This stacked low
redshift AGN spectrum is remarkably similar in shape to the XRB spectrum (when
shifted to z~1), but the observed proportions of different absorption
populations differ from most XRB synthesis models. AGN with Compton-thick
absorption account for only ~12% of the sample, but produce a significant
contribution to the overall spectrum. We confirm that Compton reflection is
more prominent in moderately-absorbed AGN and that the photon index differs
intrinsically between unabsorbed and absorbed AGN. The AGN in our sample
account for only ~1% of the XRB intensity. The reproduction of the XRB spectral
shape suggests that strong evolution in individual AGN properties is not
required between z~0 and 1.
An XMM-Newton Survey of the Soft X-ray Background. III. The Galactic Halo X-ray Emission. (arXiv:1306.2312v1 [astro-ph.GA])
An XMM-Newton Survey of the Soft X-ray Background. III. The Galactic Halo X-ray Emission. (arXiv:1306.2312v1 [astro-ph.GA]):
We present measurements of the Galactic halo's X-ray emission for 110
XMM-Newton sight lines, selected to minimize contamination from solar wind
charge exchange emission. We detect emission from few million degree gas on
~4/5 of our sight lines. The temperature is fairly uniform (median = 2.22e6 K,
interquartile range = 0.63e6 K), while the emission measure and intrinsic
0.5--2.0 keV surface brightness vary by over an order of magnitude (~(0.4-7)e-3
cm^-6 pc and ~(0.5-7)e-12 erg cm^-2 s^-1 deg^-2, respectively, with median
detections of 1.9e-3 cm^-6 pc and 1.5e-12 erg cm^-2 s^-1 deg^-2, respectively).
The high-latitude sky contains a patchy distribution of few million degree gas.
This gas exhibits a general increase in emission measure toward the inner
Galaxy in the southern Galactic hemisphere. However, there is no tendency for
our observed emission measures to decrease with increasing Galactic latitude,
contrary to what is expected for a disk-like halo morphology. The measured
temperatures, brightnesses, and spatial distributions of the gas can be used to
place constraints on models for the dominant heating sources of the halo. We
provide some discussion of such heating sources, but defer comparisons between
the observations and detailed models to a later paper.
We present measurements of the Galactic halo's X-ray emission for 110
XMM-Newton sight lines, selected to minimize contamination from solar wind
charge exchange emission. We detect emission from few million degree gas on
~4/5 of our sight lines. The temperature is fairly uniform (median = 2.22e6 K,
interquartile range = 0.63e6 K), while the emission measure and intrinsic
0.5--2.0 keV surface brightness vary by over an order of magnitude (~(0.4-7)e-3
cm^-6 pc and ~(0.5-7)e-12 erg cm^-2 s^-1 deg^-2, respectively, with median
detections of 1.9e-3 cm^-6 pc and 1.5e-12 erg cm^-2 s^-1 deg^-2, respectively).
The high-latitude sky contains a patchy distribution of few million degree gas.
This gas exhibits a general increase in emission measure toward the inner
Galaxy in the southern Galactic hemisphere. However, there is no tendency for
our observed emission measures to decrease with increasing Galactic latitude,
contrary to what is expected for a disk-like halo morphology. The measured
temperatures, brightnesses, and spatial distributions of the gas can be used to
place constraints on models for the dominant heating sources of the halo. We
provide some discussion of such heating sources, but defer comparisons between
the observations and detailed models to a later paper.
Transit observations of the Hot Jupiter HD 189733b at X-ray wavelengths. (arXiv:1306.2311v1 [astro-ph.SR])
Transit observations of the Hot Jupiter HD 189733b at X-ray wavelengths. (arXiv:1306.2311v1 [astro-ph.SR]):
We present new X-ray observations obtained with Chandra ACIS-S of the HD
189733 system, consisting of a K-type star orbited by a transiting Hot Jupiter
and an M-type stellar companion. We report a detection of the planetary transit
in soft X-rays with a significantly larger transit depth than observed in the
optical. The X-ray data favor a transit depth of 6-8%, versus a broadband
optical transit depth of 2.41%. While we are able to exclude several possible
stellar origins for this deep transit, additional observations will be
necessary to fully exclude the possibility that coronal inhomogeneities
influence the result. From the available data, we interpret the deep X-ray
transit to be caused by a thin outer planetary atmosphere which is transparent
at optical wavelengths, but dense enough to be opaque to X-rays. The X-ray
radius appears to be larger than the radius observed at far-UV wavelengths,
most likely due to high temperatures in the outer atmosphere at which hydrogen
is mostly ionized. We furthermore detect the stellar companion HD 189733B in
X-rays for the first time with an X-ray luminosity of log LX = 26.67 erg/s. We
show that the magnetic activity level of the companion is at odds with the
activity level observed for the planet-hosting primary. The discrepancy may be
caused by tidal interaction between the Hot Jupiter and its host star.
We present new X-ray observations obtained with Chandra ACIS-S of the HD
189733 system, consisting of a K-type star orbited by a transiting Hot Jupiter
and an M-type stellar companion. We report a detection of the planetary transit
in soft X-rays with a significantly larger transit depth than observed in the
optical. The X-ray data favor a transit depth of 6-8%, versus a broadband
optical transit depth of 2.41%. While we are able to exclude several possible
stellar origins for this deep transit, additional observations will be
necessary to fully exclude the possibility that coronal inhomogeneities
influence the result. From the available data, we interpret the deep X-ray
transit to be caused by a thin outer planetary atmosphere which is transparent
at optical wavelengths, but dense enough to be opaque to X-rays. The X-ray
radius appears to be larger than the radius observed at far-UV wavelengths,
most likely due to high temperatures in the outer atmosphere at which hydrogen
is mostly ionized. We furthermore detect the stellar companion HD 189733B in
X-rays for the first time with an X-ray luminosity of log LX = 26.67 erg/s. We
show that the magnetic activity level of the companion is at odds with the
activity level observed for the planet-hosting primary. The discrepancy may be
caused by tidal interaction between the Hot Jupiter and its host star.
The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission. (arXiv:1306.2307v1 [astro-ph.HE])
The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission. (arXiv:1306.2307v1 [astro-ph.HE]):
This White Paper, submitted to the recent ESA call for science themes to
define its future large missions, advocates the need for a transformational
leap in our understanding of two key questions in astrophysics: 1) How does
ordinary matter assemble into the large scale structures that we see today? 2)
How do black holes grow and shape the Universe? Hot gas in clusters, groups and
the intergalactic medium dominates the baryonic content of the local Universe.
To understand the astrophysical processes responsible for the formation and
assembly of these large structures, it is necessary to measure their physical
properties and evolution. This requires spatially resolved X-ray spectroscopy
with a factor 10 increase in both telescope throughput and spatial resolving
power compared to currently planned facilities. Feedback from supermassive
black holes is an essential ingredient in this process and in most galaxy
evolution models, but it is not well understood. X-ray observations can
uniquely reveal the mechanisms launching winds close to black holes and
determine the coupling of the energy and matter flows on larger scales. Due to
the effects of feedback, a complete understanding of galaxy evolution requires
knowledge of the obscured growth of supermassive black holes through cosmic
time, out to the redshifts where the first galaxies form. X-ray emission is the
most reliable way to reveal accreting black holes, but deep survey speed must
improve by a factor ~100 over current facilities to perform a full census into
the early Universe. The Advanced Telescope for High Energy Astrophysics
(Athena+) mission provides the necessary performance (e.g. angular resolution,
spectral resolution, survey grasp) to address these questions and revolutionize
our understanding of the Hot and Energetic Universe. These capabilities will
also provide a powerful observatory to be used in all areas of astrophysics.
This White Paper, submitted to the recent ESA call for science themes to
define its future large missions, advocates the need for a transformational
leap in our understanding of two key questions in astrophysics: 1) How does
ordinary matter assemble into the large scale structures that we see today? 2)
How do black holes grow and shape the Universe? Hot gas in clusters, groups and
the intergalactic medium dominates the baryonic content of the local Universe.
To understand the astrophysical processes responsible for the formation and
assembly of these large structures, it is necessary to measure their physical
properties and evolution. This requires spatially resolved X-ray spectroscopy
with a factor 10 increase in both telescope throughput and spatial resolving
power compared to currently planned facilities. Feedback from supermassive
black holes is an essential ingredient in this process and in most galaxy
evolution models, but it is not well understood. X-ray observations can
uniquely reveal the mechanisms launching winds close to black holes and
determine the coupling of the energy and matter flows on larger scales. Due to
the effects of feedback, a complete understanding of galaxy evolution requires
knowledge of the obscured growth of supermassive black holes through cosmic
time, out to the redshifts where the first galaxies form. X-ray emission is the
most reliable way to reveal accreting black holes, but deep survey speed must
improve by a factor ~100 over current facilities to perform a full census into
the early Universe. The Advanced Telescope for High Energy Astrophysics
(Athena+) mission provides the necessary performance (e.g. angular resolution,
spectral resolution, survey grasp) to address these questions and revolutionize
our understanding of the Hot and Energetic Universe. These capabilities will
also provide a powerful observatory to be used in all areas of astrophysics.
The Hot and Energetic Universe: The evolution of galaxy groups and clusters. (arXiv:1306.2319v1 [astro-ph.HE])
The Hot and Energetic Universe: The evolution of galaxy groups and clusters. (arXiv:1306.2319v1 [astro-ph.HE]):
Major astrophysical questions related to the formation and evolution of
structures, and more specifically of galaxy groups and clusters, will still be
open in the coming decade and beyond: what is the interplay of galaxy,
supermassive black hole, and intergalactic gas evolution in the most massive
objects in the Universe - galaxy groups and clusters? What are the processes
driving the evolution of chemical enrichment of the hot diffuse gas in
large-scale structures? How and when did the first galaxy groups in the
Universe, massive enough to bind more than 10^7 K gas, form? Focussing on the
period when groups and clusters assembled (0.5<z<2.5), we show that, due to the
continuum and line emission of this hot intergalactic gas at X-ray wavelengths,
Athena+, combining high sensitivity with excellent spectral and spatial
resolution, will deliver breakthrough observations in view of the
aforementioned issues. Indeed, the physical and chemical properties of the hot
intra-cluster gas, and their evolution across time, are a key to understand the
co-evolution of galaxy and supermassive black hole within their environments.
Major astrophysical questions related to the formation and evolution of
structures, and more specifically of galaxy groups and clusters, will still be
open in the coming decade and beyond: what is the interplay of galaxy,
supermassive black hole, and intergalactic gas evolution in the most massive
objects in the Universe - galaxy groups and clusters? What are the processes
driving the evolution of chemical enrichment of the hot diffuse gas in
large-scale structures? How and when did the first galaxy groups in the
Universe, massive enough to bind more than 10^7 K gas, form? Focussing on the
period when groups and clusters assembled (0.5<z<2.5), we show that, due to the
continuum and line emission of this hot intergalactic gas at X-ray wavelengths,
Athena+, combining high sensitivity with excellent spectral and spatial
resolution, will deliver breakthrough observations in view of the
aforementioned issues. Indeed, the physical and chemical properties of the hot
intra-cluster gas, and their evolution across time, are a key to understand the
co-evolution of galaxy and supermassive black hole within their environments.
The Hot and Energetic Universe: The astrophysics of galaxy groups and clusters. (arXiv:1306.2322v1 [astro-ph.HE])
The Hot and Energetic Universe: The astrophysics of galaxy groups and clusters. (arXiv:1306.2322v1 [astro-ph.HE]):
As the nodes of the cosmic web, clusters of galaxies trace the large-scale
distribution of matter in the Universe. They are thus privileged sites in which
to investigate the complex physics of structure formation. However, the
complete story of how these structures grow, and how they dissipate the
gravitational and non-thermal components of their energy budget over cosmic
time, is still beyond our grasp. Fundamental questions such as How do hot
diffuse baryons accrete and dynamically evolve in dark matter potentials? How
and when was the energy that we observe in the ICM generated and distributed?
Where and when are heavy elements produced and how are they circulated? are
still unanswered. Most of the cluster baryons exists in the form of a diffuse,
hot, metal-enriched plasma that radiates primarily in the X-ray band (the
intracluster medium, ICM), allowing the X-ray observations of the evolving
cluster population to provide a unique opportunity to address these topics.
Athena+ with its large collecting area and unprecedented combination of high
spectral and angular resolution offers the only way to make major advances in
answering these questions. Athena+ will show how the baryonic gas evolves in
the dark matter potential wells by studying the motions and turbulence in the
ICM. Athena+ will be able to resolve the accreting region both spatially and
spectroscopically, probing the true nature and physical state of the X-ray
emitting plasma. Athena+ has the capabilities to permit a definitive
understanding of the formation and evolution of large-scale cosmic structure
through the study of the cluster population.
As the nodes of the cosmic web, clusters of galaxies trace the large-scale
distribution of matter in the Universe. They are thus privileged sites in which
to investigate the complex physics of structure formation. However, the
complete story of how these structures grow, and how they dissipate the
gravitational and non-thermal components of their energy budget over cosmic
time, is still beyond our grasp. Fundamental questions such as How do hot
diffuse baryons accrete and dynamically evolve in dark matter potentials? How
and when was the energy that we observe in the ICM generated and distributed?
Where and when are heavy elements produced and how are they circulated? are
still unanswered. Most of the cluster baryons exists in the form of a diffuse,
hot, metal-enriched plasma that radiates primarily in the X-ray band (the
intracluster medium, ICM), allowing the X-ray observations of the evolving
cluster population to provide a unique opportunity to address these topics.
Athena+ with its large collecting area and unprecedented combination of high
spectral and angular resolution offers the only way to make major advances in
answering these questions. Athena+ will show how the baryonic gas evolves in
the dark matter potential wells by studying the motions and turbulence in the
ICM. Athena+ will be able to resolve the accreting region both spatially and
spectroscopically, probing the true nature and physical state of the X-ray
emitting plasma. Athena+ has the capabilities to permit a definitive
understanding of the formation and evolution of large-scale cosmic structure
through the study of the cluster population.
The Hot and Energetic Universe: AGN feedback in galaxy clusters and groups. (arXiv:1306.2323v1 [astro-ph.HE])
The Hot and Energetic Universe: AGN feedback in galaxy clusters and groups. (arXiv:1306.2323v1 [astro-ph.HE]):
Mechanical feedback via Active Galactic Nuclei (AGN) jets in the centres of
galaxy groups and clusters is a crucial ingredient in current models of galaxy
formation and cluster evolution. Jet feedback is believed to regulate gas
cooling and thus star formation in the most massive galaxies, but a robust
physical understanding of this feedback mode is currently lacking. The large
collecting area, excellent spectral resolution and high spatial resolution of
Athena+ will provide the breakthrough diagnostic ability necessary to develop
this understanding, via: (1) the first kinematic measurements on relevant
spatial scales of the hot gas in galaxy, group and cluster haloes as it absorbs
the impact of AGN jets, and (2) vastly improved ability to map thermodynamic
conditions on scales well-matched to the jets, lobes and gas disturbances
produced by them. Athena+ will therefore determine for the first time how jet
energy is dissipated and distributed in group and cluster gas, and how a
feedback loop operates in group/cluster cores to regulate gas cooling and AGN
fuelling. Athena+ will also establish firmly the cumulative impact of powerful
radio galaxies on the evolution of baryons from the epoch of group/cluster
formation to the present day.
Mechanical feedback via Active Galactic Nuclei (AGN) jets in the centres of
galaxy groups and clusters is a crucial ingredient in current models of galaxy
formation and cluster evolution. Jet feedback is believed to regulate gas
cooling and thus star formation in the most massive galaxies, but a robust
physical understanding of this feedback mode is currently lacking. The large
collecting area, excellent spectral resolution and high spatial resolution of
Athena+ will provide the breakthrough diagnostic ability necessary to develop
this understanding, via: (1) the first kinematic measurements on relevant
spatial scales of the hot gas in galaxy, group and cluster haloes as it absorbs
the impact of AGN jets, and (2) vastly improved ability to map thermodynamic
conditions on scales well-matched to the jets, lobes and gas disturbances
produced by them. Athena+ will therefore determine for the first time how jet
energy is dissipated and distributed in group and cluster gas, and how a
feedback loop operates in group/cluster cores to regulate gas cooling and AGN
fuelling. Athena+ will also establish firmly the cumulative impact of powerful
radio galaxies on the evolution of baryons from the epoch of group/cluster
formation to the present day.
The Hot and Energetic Universe: The missing baryons and the warm-hot intergalactic medium. (arXiv:1306.2324v1 [astro-ph.HE])
The Hot and Energetic Universe: The missing baryons and the warm-hot intergalactic medium. (arXiv:1306.2324v1 [astro-ph.HE]):
The backbone of the large-scale structure of the Universe is determined by
processes on a cosmological scale and by the gravitational interaction of the
dominant dark matter. However, the mobile baryon population shapes the
appearance of these structures. Theory predicts that most of the baryons reside
in vast unvirialized filamentary structures that connect galaxy groups and
clusters, but the observational evidence is currently lacking. Because the
majority of the baryons are supposed to exist in a large-scale, hot and dilute
gaseous phase, X-rays provide the ideal tool to progress our understanding.
Observations with the Athena+ X-ray Integral Field Unit will reveal the
location, chemical composition, physical state and dynamics of the active
population of baryons.
The backbone of the large-scale structure of the Universe is determined by
processes on a cosmological scale and by the gravitational interaction of the
dominant dark matter. However, the mobile baryon population shapes the
appearance of these structures. Theory predicts that most of the baryons reside
in vast unvirialized filamentary structures that connect galaxy groups and
clusters, but the observational evidence is currently lacking. Because the
majority of the baryons are supposed to exist in a large-scale, hot and dilute
gaseous phase, X-rays provide the ideal tool to progress our understanding.
Observations with the Athena+ X-ray Integral Field Unit will reveal the
location, chemical composition, physical state and dynamics of the active
population of baryons.
The Hot and Energetic Universe: The formation and growth of the earliest supermassive black holes. (arXiv:1306.2325v1 [astro-ph.HE])
The Hot and Energetic Universe: The formation and growth of the earliest supermassive black holes. (arXiv:1306.2325v1 [astro-ph.HE]):
A crucial challenge in astrophysics over the coming decades will be to
understand the origins of supermassive black holes (SMBHs) that lie at the
centres of most, if not all, galaxies. The processes responsible for the
initial formation of these SMBHs and their early growth via accretion - when
they are seen as Active Galactic Nuclei (AGN) - remain unknown. To address this
challenge, we must identify low luminosity and obscured z>6 AGNs, which
represent the bulk of early SMBH growth. Sensitive X-ray observations are a
unique signpost of accretion activity, uncontaminated by star formation
processes, which prevent reliable AGN identification at other wavelengths (e.g.
optical, infrared). The Athena+ Wide Field Imager will enable X-ray surveys to
be carried out two orders of magnitude faster than with Chandra or XMM-Newton,
opening a new discovery space and identifying over 400 z>6 AGN, including
obscured sources. Athena+ will also play a fundamental role to enhance the
scientific return of future multiwavelength facilities that will probe the
physical conditions within the host galaxies of early SMBHs, which is vital for
understanding how SMBHs form, what fuels their subsequent growth, and to assess
their impact on the early Universe. Follow-up of samples of z>6 galaxies with
the Athena+ X-ray Integral Field Unit could also reveal the presence of highly
obscured AGNs, thanks to the detection of strong iron lines. Thus, Athena+ will
enable the first quantitative measurements of the extent and distribution of
SMBH accretion in the early Universe.
A crucial challenge in astrophysics over the coming decades will be to
understand the origins of supermassive black holes (SMBHs) that lie at the
centres of most, if not all, galaxies. The processes responsible for the
initial formation of these SMBHs and their early growth via accretion - when
they are seen as Active Galactic Nuclei (AGN) - remain unknown. To address this
challenge, we must identify low luminosity and obscured z>6 AGNs, which
represent the bulk of early SMBH growth. Sensitive X-ray observations are a
unique signpost of accretion activity, uncontaminated by star formation
processes, which prevent reliable AGN identification at other wavelengths (e.g.
optical, infrared). The Athena+ Wide Field Imager will enable X-ray surveys to
be carried out two orders of magnitude faster than with Chandra or XMM-Newton,
opening a new discovery space and identifying over 400 z>6 AGN, including
obscured sources. Athena+ will also play a fundamental role to enhance the
scientific return of future multiwavelength facilities that will probe the
physical conditions within the host galaxies of early SMBHs, which is vital for
understanding how SMBHs form, what fuels their subsequent growth, and to assess
their impact on the early Universe. Follow-up of samples of z>6 galaxies with
the Athena+ X-ray Integral Field Unit could also reveal the presence of highly
obscured AGNs, thanks to the detection of strong iron lines. Thus, Athena+ will
enable the first quantitative measurements of the extent and distribution of
SMBH accretion in the early Universe.
The Hot and Energetic Universe: Understanding the build-up of supermassive black holes and galaxies at the heyday of the Universe. (arXiv:1306.2328v1 [astro-ph.HE])
The Hot and Energetic Universe: Understanding the build-up of supermassive black holes and galaxies at the heyday of the Universe. (arXiv:1306.2328v1 [astro-ph.HE]):
Observations in the last decade have provided strong evidence that the growth
of supermassive black holes at the centres of galaxies is among the most
influential processes in galaxy evolution. Open questions that relate to our
current understanding of black hole growth and its relation to the build-up of
galaxies at redshifts z=1-4, when most black holes and stars we see in
present-day galaxies were put in place, include: what is the nature of AGN
feedback and whether it plays a significant role in the evolution of galaxies?
what is the dominant population of accreting AGN at that critical epoch? is it
dominated by obscured objects as required by many current observations and
models? The Athena+ mission concept will provide the technological leap
required for a breakthrough in our understanding of AGN and galaxy evolution at
the heyday of the Universe. The high throughput of Athena+ will allow the
systematic study of the incidence, nature and energetics of AGN feedback
processes to z~4 via the identification and measurement of blue-shifted X-ray
absorption lines. The excellent survey and spectral capabilities of the Athena+
Wide Field Imager will complete the census of black hole growth by yielding
samples of up to 100 times larger than is currently possible of the most
heavily obscured, including Compton thick, AGN to redshifts z~4. The
demographics of this population relative to their hosts is fundamental for
understanding how major black hole growth events relate to the build-up of
galaxies.
Observations in the last decade have provided strong evidence that the growth
of supermassive black holes at the centres of galaxies is among the most
influential processes in galaxy evolution. Open questions that relate to our
current understanding of black hole growth and its relation to the build-up of
galaxies at redshifts z=1-4, when most black holes and stars we see in
present-day galaxies were put in place, include: what is the nature of AGN
feedback and whether it plays a significant role in the evolution of galaxies?
what is the dominant population of accreting AGN at that critical epoch? is it
dominated by obscured objects as required by many current observations and
models? The Athena+ mission concept will provide the technological leap
required for a breakthrough in our understanding of AGN and galaxy evolution at
the heyday of the Universe. The high throughput of Athena+ will allow the
systematic study of the incidence, nature and energetics of AGN feedback
processes to z~4 via the identification and measurement of blue-shifted X-ray
absorption lines. The excellent survey and spectral capabilities of the Athena+
Wide Field Imager will complete the census of black hole growth by yielding
samples of up to 100 times larger than is currently possible of the most
heavily obscured, including Compton thick, AGN to redshifts z~4. The
demographics of this population relative to their hosts is fundamental for
understanding how major black hole growth events relate to the build-up of
galaxies.
The Hot and Energetic Universe: Astrophysics of feedback in local AGN. (arXiv:1306.2330v1 [astro-ph.HE])
The Hot and Energetic Universe: Astrophysics of feedback in local AGN. (arXiv:1306.2330v1 [astro-ph.HE]):
Understanding the astrophysics of feedback in active galactic nuclei (AGN) is
key to understanding the growth and co-evolution of supermassive black holes
and galaxies. AGN-driven winds/outflows are potentially the most effective way
of transporting energy and momentum from the nuclear scales to the host galaxy,
quenching star formation by sweeping away the gas reservoir. Key questions in
this field are: 1) how do accretion disks around black holes launch
winds/outflows, and how much energy do these carry? 2) How are the energy and
metals accelerated in winds/outflows transferred and deposited into the
circumgalactic medium? X-ray observations are a unique way to address these
questions because they probe the phase of the outflows which carries most of
the kinetic energy. We show how a high throughput, high spectral resolution
instrument like the X-ray Integral Field Unit (X-IFU) on Athena+ will allow us
to address these questions by determining the physical parameters (ionization
state, density, temperature, abundances, velocities, geometry, etc.) of the
outflows on a dynamical time-scale, in a broad sample of nearby bright AGN. The
X-IFU will also allow direct spectral imaging of the impact of these winds on
the host galaxy for local AGN, forming a template for understanding AGN at
higher redshifts where wind shocks cannot be resolved.
Understanding the astrophysics of feedback in active galactic nuclei (AGN) is
key to understanding the growth and co-evolution of supermassive black holes
and galaxies. AGN-driven winds/outflows are potentially the most effective way
of transporting energy and momentum from the nuclear scales to the host galaxy,
quenching star formation by sweeping away the gas reservoir. Key questions in
this field are: 1) how do accretion disks around black holes launch
winds/outflows, and how much energy do these carry? 2) How are the energy and
metals accelerated in winds/outflows transferred and deposited into the
circumgalactic medium? X-ray observations are a unique way to address these
questions because they probe the phase of the outflows which carries most of
the kinetic energy. We show how a high throughput, high spectral resolution
instrument like the X-ray Integral Field Unit (X-IFU) on Athena+ will allow us
to address these questions by determining the physical parameters (ionization
state, density, temperature, abundances, velocities, geometry, etc.) of the
outflows on a dynamical time-scale, in a broad sample of nearby bright AGN. The
X-IFU will also allow direct spectral imaging of the impact of these winds on
the host galaxy for local AGN, forming a template for understanding AGN at
higher redshifts where wind shocks cannot be resolved.
The Hot and Energetic Universe: The close environments of supermassive black holes. (arXiv:1306.2331v1 [astro-ph.HE])
The Hot and Energetic Universe: The close environments of supermassive black holes. (arXiv:1306.2331v1 [astro-ph.HE]):
Most of the action in Active Galactic Nuclei (AGN) occurs within a few tens
of gravitational radii from the supermassive black hole, where matter in the
accretion disk may lose up to almost half of its energy with a copious
production of X-rays, emitted via Comptonization of the disk photons by hot
electrons in a corona and partly reflected by the accretion disk. Thanks to its
large effective area and excellent energy resolution, Athena+ contributions in
the understanding of the physics of accretion in AGN will be fundamental - and
unique - in many respects. It will allow us to map the disk-corona system -
which is crucial to understand the mechanism of energy extraction and the
relation of the corona with winds and jets - by studying the time lags between
reflected and primary photons. These lags have been recently discovered by
XMM-Newton, but only Athena+ will have the sensitivity required to fully
exploit this technique. Athena+ will also be able e.g. to determine robustly
the spin of the black hole in nearby sources (and to extend these measurements
beyond the local Universe), to establish the nature of the soft X-ray
components, and to map the circumnuclear matter within the AGN inner parsec
with unprecedented details.
Most of the action in Active Galactic Nuclei (AGN) occurs within a few tens
of gravitational radii from the supermassive black hole, where matter in the
accretion disk may lose up to almost half of its energy with a copious
production of X-rays, emitted via Comptonization of the disk photons by hot
electrons in a corona and partly reflected by the accretion disk. Thanks to its
large effective area and excellent energy resolution, Athena+ contributions in
the understanding of the physics of accretion in AGN will be fundamental - and
unique - in many respects. It will allow us to map the disk-corona system -
which is crucial to understand the mechanism of energy extraction and the
relation of the corona with winds and jets - by studying the time lags between
reflected and primary photons. These lags have been recently discovered by
XMM-Newton, but only Athena+ will have the sensitivity required to fully
exploit this technique. Athena+ will also be able e.g. to determine robustly
the spin of the black hole in nearby sources (and to extend these measurements
beyond the local Universe), to establish the nature of the soft X-ray
components, and to map the circumnuclear matter within the AGN inner parsec
with unprecedented details.
The Hot and Energetic Universe: Solar system and exoplanets. (arXiv:1306.2332v1 [astro-ph.HE])
The Hot and Energetic Universe: Solar system and exoplanets. (arXiv:1306.2332v1 [astro-ph.HE]):
The high resolution non-dispersive spectroscopy and unprecedented sensitivity
of Athena+ will revolutionize solar system observing: the origin of the ions
producing Jupiter's X-ray aurorae via charge exchange will be conclusively
established, as well as their dynamics, giving clues to their acceleration
mechanisms. X-ray aurorae on Saturn will be searched for to a depth
unattainable by current Earth-bound observatories. The X-ray Integral Field
Unit of Athena+ will map Mars' expanding exosphere, which has a line-rich solar
wind charge exchange spectrum, under differing solar wind conditions and
through the seasons; relating Mars' X-ray emission to its atmospheric loss will
have significant impact also on the study of exoplanet atmospheres. Spectral
mapping of cometary comae, which are spectacular X-ray sources with extremely
line-rich spectra, will probe solar wind composition and speed at varying
distances from the Sun. Athena+ will provide unique contributions also to
exoplanetary astrophysics. Athena+ will pioneer the study of
ingress/eclipse/egress effects during planetary orbits of hot-Jupiters, and
will confirm/improve the evidence of Star-Planet Interactions (SPI) in a wider
sample of planetary systems. Finally Athena+ will drastically improve the
knowledge of the X-ray incident radiation on exoplanets, a key element for
understanding the effects of atmospheric mass loss and of the chemical and
physical evolution of planet atmospheres, particularly relevant in the case of
young systems.
The high resolution non-dispersive spectroscopy and unprecedented sensitivity
of Athena+ will revolutionize solar system observing: the origin of the ions
producing Jupiter's X-ray aurorae via charge exchange will be conclusively
established, as well as their dynamics, giving clues to their acceleration
mechanisms. X-ray aurorae on Saturn will be searched for to a depth
unattainable by current Earth-bound observatories. The X-ray Integral Field
Unit of Athena+ will map Mars' expanding exosphere, which has a line-rich solar
wind charge exchange spectrum, under differing solar wind conditions and
through the seasons; relating Mars' X-ray emission to its atmospheric loss will
have significant impact also on the study of exoplanet atmospheres. Spectral
mapping of cometary comae, which are spectacular X-ray sources with extremely
line-rich spectra, will probe solar wind composition and speed at varying
distances from the Sun. Athena+ will provide unique contributions also to
exoplanetary astrophysics. Athena+ will pioneer the study of
ingress/eclipse/egress effects during planetary orbits of hot-Jupiters, and
will confirm/improve the evidence of Star-Planet Interactions (SPI) in a wider
sample of planetary systems. Finally Athena+ will drastically improve the
knowledge of the X-ray incident radiation on exoplanets, a key element for
understanding the effects of atmospheric mass loss and of the chemical and
physical evolution of planet atmospheres, particularly relevant in the case of
young systems.
The Hot and Energetic Universe: Star formation and evolution. (arXiv:1306.2333v1 [astro-ph.HE])
The Hot and Energetic Universe: Star formation and evolution. (arXiv:1306.2333v1 [astro-ph.HE]):
Stars over a wide range of masses and evolutionary stages are nowadays known
to emit X-rays. This X-ray emission is a unique probe of the most energetic
phenomena occurring in the circumstellar environment of these stars, and
provides precious insight on magnetic phenomena or hydrodynamic shocks. Owing
to its large collecting area, Athena+ will open up an entirely new window on
these phenomena. Indeed, Athena+ will not only allow us to study many more
objects with an unprecedented spectral resolution, but will also pioneer the
study of the dynamics of these objects via time-resolved high-resolution
spectroscopy. In this way, Athena+ will be a unique tool to study accretion
processes in TTauri stars, flaring activity in young stars, dynamos in
ultra-cool dwarfs, small and large-scale structures in the winds of single
massive stars, wind interactions in massive binary systems, hot bubbles in
planetary nebula... All these studies will lead to a deeper understanding of
yet poorly understood processes which have profound impact in star and
planetary system formation as well as in feedback processes on Galactic scale.
Stars over a wide range of masses and evolutionary stages are nowadays known
to emit X-rays. This X-ray emission is a unique probe of the most energetic
phenomena occurring in the circumstellar environment of these stars, and
provides precious insight on magnetic phenomena or hydrodynamic shocks. Owing
to its large collecting area, Athena+ will open up an entirely new window on
these phenomena. Indeed, Athena+ will not only allow us to study many more
objects with an unprecedented spectral resolution, but will also pioneer the
study of the dynamics of these objects via time-resolved high-resolution
spectroscopy. In this way, Athena+ will be a unique tool to study accretion
processes in TTauri stars, flaring activity in young stars, dynamos in
ultra-cool dwarfs, small and large-scale structures in the winds of single
massive stars, wind interactions in massive binary systems, hot bubbles in
planetary nebula... All these studies will lead to a deeper understanding of
yet poorly understood processes which have profound impact in star and
planetary system formation as well as in feedback processes on Galactic scale.
The Hot and Energetic Universe: End points of stellar evolution. (arXiv:1306.2334v1 [astro-ph.HE])
The Hot and Energetic Universe: End points of stellar evolution. (arXiv:1306.2334v1 [astro-ph.HE]):
White dwarfs, neutron stars and stellar mass black holes are key laboratories
to study matter in most extreme conditions of gravity and magnetic field. The
unprecedented effective area of Athena+ will allow us to advance our
understanding of emission mechanisms and accretion physics over a wide range of
mass accretion rates, starting from lower and sub-luminous quiescent X-ray
binaries up to super-Eddington ultra-luminous sources. Athena+ will measure
stellar black hole spins in a much higher number of binaries than achievable
now, opening the possibility to study how spin varies with black hole history.
The high throughput and energy resolution of the X-IFU will be instrumental in
establishing how disc wind properties depend on accretion state, in determining
wind launching mechanism and in quantifying the impact of the wind induced mass
loss on binary evolution and environment. Triggers and high quality optical and
radio data originating from large wide field contemporaneous instruments will
provide essential complementary information on jet launching mechanisms and on
the physics of rotation powered pulsars, for instance. In addition, Athena+
will furnish multiple, independent measurements of the neutron star mass/radius
relation in a wide range of environments and conditions so as to constrain the
debated equation of state.
White dwarfs, neutron stars and stellar mass black holes are key laboratories
to study matter in most extreme conditions of gravity and magnetic field. The
unprecedented effective area of Athena+ will allow us to advance our
understanding of emission mechanisms and accretion physics over a wide range of
mass accretion rates, starting from lower and sub-luminous quiescent X-ray
binaries up to super-Eddington ultra-luminous sources. Athena+ will measure
stellar black hole spins in a much higher number of binaries than achievable
now, opening the possibility to study how spin varies with black hole history.
The high throughput and energy resolution of the X-IFU will be instrumental in
establishing how disc wind properties depend on accretion state, in determining
wind launching mechanism and in quantifying the impact of the wind induced mass
loss on binary evolution and environment. Triggers and high quality optical and
radio data originating from large wide field contemporaneous instruments will
provide essential complementary information on jet launching mechanisms and on
the physics of rotation powered pulsars, for instance. In addition, Athena+
will furnish multiple, independent measurements of the neutron star mass/radius
relation in a wide range of environments and conditions so as to constrain the
debated equation of state.
The Hot and Energetic Universe: The astrophysics of supernova remnants and the interstellar medium. (arXiv:1306.2335v1 [astro-ph.HE])
The Hot and Energetic Universe: The astrophysics of supernova remnants and the interstellar medium. (arXiv:1306.2335v1 [astro-ph.HE]):
The study of both supernova remnants and the hot and cold phases of the
interstellar medium are essential for understanding the final stages of stellar
evolution and their feedback on the evolution of galaxies through injection of
energy and heavy elements. These studies are also crucial for understanding the
physics of supernovae, their cosmological implication, and the origin of
galactic cosmic rays. The unique capabilities of Athena+ will allow us to
explore a new parameter space. Spatially-resolved high-resolution spectroscopy
using Athena+ X-IFU of young remnants will allow to characterize individual
parcels of ejected material in the line of sight in terms of kinematics,
ionization and composition, providing access to the three dimensional geometry
of the explosion. Athena+ will also allow studying shock physics and particle
acceleration in supernova remnants, as well as their interaction with their
environment. Athena+ X-IFU will also characterize the ionization mechanisms
competing in forming the complex structures of the hot interstellar medium,
likely to keep the echo of past star formation activity, both in our Galaxy and
nearby ones. For the first time the dust and gas of the densest cold medium,
like in the Galactic Centre environment, will be studied. Athena+ X-IFU will
observe, along with the Mg K and Si K edges, which are the main tracers of the
silicates content of the ISM, the Fe K edge with unprecedented sensitivity and
energy-resolution. This will allow us to study for the first time the nature of
Fe-bearing dust in such regions.
The study of both supernova remnants and the hot and cold phases of the
interstellar medium are essential for understanding the final stages of stellar
evolution and their feedback on the evolution of galaxies through injection of
energy and heavy elements. These studies are also crucial for understanding the
physics of supernovae, their cosmological implication, and the origin of
galactic cosmic rays. The unique capabilities of Athena+ will allow us to
explore a new parameter space. Spatially-resolved high-resolution spectroscopy
using Athena+ X-IFU of young remnants will allow to characterize individual
parcels of ejected material in the line of sight in terms of kinematics,
ionization and composition, providing access to the three dimensional geometry
of the explosion. Athena+ will also allow studying shock physics and particle
acceleration in supernova remnants, as well as their interaction with their
environment. Athena+ X-IFU will also characterize the ionization mechanisms
competing in forming the complex structures of the hot interstellar medium,
likely to keep the echo of past star formation activity, both in our Galaxy and
nearby ones. For the first time the dust and gas of the densest cold medium,
like in the Galactic Centre environment, will be studied. Athena+ X-IFU will
observe, along with the Mg K and Si K edges, which are the main tracers of the
silicates content of the ISM, the Fe K edge with unprecedented sensitivity and
energy-resolution. This will allow us to study for the first time the nature of
Fe-bearing dust in such regions.
The Hot and Energetic Universe: Luminous extragalactic transients. (arXiv:1306.2336v1 [astro-ph.HE])
The Hot and Energetic Universe: Luminous extragalactic transients. (arXiv:1306.2336v1 [astro-ph.HE]):
We discuss the importance and potential contribution of Athena+ to the
science questions related to gamma-ray bursts, tidal disruption events and
supernova shock break-out. Athena+ will allow breakthrough observations
involving high-resolution X-ray spectroscopic observations of high-z gamma-ray
bursts, observations of tidal disruption events tailored to determine the mass
and potentially the spin of the black hole responsible for the tidal disruption
and observations of X-rays from the supernova shock breakout providing a
measure of the radius of the exploding star or of the companion in the case of
type Ia supernovae. We briefly discuss survey facilities that will provide
triggers to these events envisaged to be operational around 2028.
We discuss the importance and potential contribution of Athena+ to the
science questions related to gamma-ray bursts, tidal disruption events and
supernova shock break-out. Athena+ will allow breakthrough observations
involving high-resolution X-ray spectroscopic observations of high-z gamma-ray
bursts, observations of tidal disruption events tailored to determine the mass
and potentially the spin of the black hole responsible for the tidal disruption
and observations of X-rays from the supernova shock breakout providing a
measure of the radius of the exploding star or of the companion in the case of
type Ia supernovae. We briefly discuss survey facilities that will provide
triggers to these events envisaged to be operational around 2028.
Continued Neutron Star Crust Cooling of the 11 Hz X-Ray Pulsar in Terzan 5: A Challenge to Heating and Cooling Models?. (arXiv:1306.2345v1 [astro-ph.HE])
Continued Neutron Star Crust Cooling of the 11 Hz X-Ray Pulsar in Terzan 5: A Challenge to Heating and Cooling Models?. (arXiv:1306.2345v1 [astro-ph.HE]):
The transient neutron star low-mass X-ray binary and 11 Hz X-ray pulsar IGR
J17480-2446 in the globular cluster Terzan 5 exhibited an 11-week accretion
outburst in 2010. Chandra observations performed within five months after the
end of the outburst revealed evidence that the crust of the neutron star became
substantially heated during the accretion episode and was subsequently cooling
in quiescence. This provides the rare opportunity to probe the structure and
composition of the crust. Here, we report on new Chandra observations of Terzan
5 that extend the monitoring to ~2.2 yr into quiescence. We find that the
thermal flux and neutron star temperature have continued to decrease, but
remain significantly above the values that were measured before the 2010
accretion phase. This suggests that the crust has not thermally relaxed yet,
and may continue to cool. Such behavior is difficult to explain within our
current understanding of heating and cooling of transiently accreting neutron
stars. Alternatively, the quiescent emission may have settled at a higher
observed equilibrium level (for the same interior temperature), in which case
the neutron star crust may have fully cooled.
The transient neutron star low-mass X-ray binary and 11 Hz X-ray pulsar IGR
J17480-2446 in the globular cluster Terzan 5 exhibited an 11-week accretion
outburst in 2010. Chandra observations performed within five months after the
end of the outburst revealed evidence that the crust of the neutron star became
substantially heated during the accretion episode and was subsequently cooling
in quiescence. This provides the rare opportunity to probe the structure and
composition of the crust. Here, we report on new Chandra observations of Terzan
5 that extend the monitoring to ~2.2 yr into quiescence. We find that the
thermal flux and neutron star temperature have continued to decrease, but
remain significantly above the values that were measured before the 2010
accretion phase. This suggests that the crust has not thermally relaxed yet,
and may continue to cool. Such behavior is difficult to explain within our
current understanding of heating and cooling of transiently accreting neutron
stars. Alternatively, the quiescent emission may have settled at a higher
observed equilibrium level (for the same interior temperature), in which case
the neutron star crust may have fully cooled.
Discovery of high-frequency iron K lags in Ark 564 and Mrk 335. (arXiv:1306.2551v1 [astro-ph.HE])
Discovery of high-frequency iron K lags in Ark 564 and Mrk 335. (arXiv:1306.2551v1 [astro-ph.HE]):
We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate
the frequency dependent time-lags for these two well-studied sources. We
discover high-frequency Fe K lags in both sources, indicating that the red wing
of the line precedes the rest frame energy by roughly 100 s and 150 s for Ark
564 and Mrk 335, respectively. Including these two new sources, Fe K
reverberation lags have been observed in seven Seyfert galaxies. We examine the
low-frequency lag-energy spectrum, which is smooth, and shows no feature of
reverberation, as would be expected if the low-frequency lags were produced by
distant reflection off circumnuclear material. The clear differences in the low
and high frequency lag-energy spectra indicate that the lags are produced by
two distinct physical processes. Finally, we find that the amplitude of the Fe
K lag scales with black hole mass for these seven sources, consistent with a
relativistic reflection model where the lag is the light travel delay
associated with reflection of continuum photons off the inner disc.
We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate
the frequency dependent time-lags for these two well-studied sources. We
discover high-frequency Fe K lags in both sources, indicating that the red wing
of the line precedes the rest frame energy by roughly 100 s and 150 s for Ark
564 and Mrk 335, respectively. Including these two new sources, Fe K
reverberation lags have been observed in seven Seyfert galaxies. We examine the
low-frequency lag-energy spectrum, which is smooth, and shows no feature of
reverberation, as would be expected if the low-frequency lags were produced by
distant reflection off circumnuclear material. The clear differences in the low
and high frequency lag-energy spectra indicate that the lags are produced by
two distinct physical processes. Finally, we find that the amplitude of the Fe
K lag scales with black hole mass for these seven sources, consistent with a
relativistic reflection model where the lag is the light travel delay
associated with reflection of continuum photons off the inner disc.
Monday, June 10, 2013
Measuring the Kerr spin parameter of a non-Kerr compact object with the continuum-fitting and the iron line methods. (arXiv:1305.5409v1 [gr-qc])
Measuring the Kerr spin parameter of a non-Kerr compact object with the continuum-fitting and the iron line methods. (arXiv:1305.5409v1 [gr-qc]):
Under the assumption that astrophysical black hole candidates are the Kerr
black holes of general relativity, the continuum-fitting method and the
analysis of the K$\alpha$ iron line are today the only available techniques
capable of providing a relatively reliable estimate of the spin parameter of
these objects. If we relax the Kerr black hole hypothesis and we try to test
the nature of black hole candidates, we find that there is a strong correlation
between the measurement of the spin and possible deviations from the Kerr
solution. The properties of the radiation emitted in a Kerr spacetime with spin
parameter $a_*$ are indeed very similar, and practically indistinguishable,
from the ones of the radiation emitted around a non-Kerr object with different
spin. In this paper, I address the question whether measuring the Kerr spin
with both the continuum-fitting method and the K$\alpha$ iron line analysis of
the same object can be used to claim the Kerr nature of the black hole
candidate in the case of consistent results. The answer is more likely
negative: if the object is not a Kerr black hole but we assume it is, the two
techniques may anyway provide a very similar result.
Under the assumption that astrophysical black hole candidates are the Kerr
black holes of general relativity, the continuum-fitting method and the
analysis of the K$\alpha$ iron line are today the only available techniques
capable of providing a relatively reliable estimate of the spin parameter of
these objects. If we relax the Kerr black hole hypothesis and we try to test
the nature of black hole candidates, we find that there is a strong correlation
between the measurement of the spin and possible deviations from the Kerr
solution. The properties of the radiation emitted in a Kerr spacetime with spin
parameter $a_*$ are indeed very similar, and practically indistinguishable,
from the ones of the radiation emitted around a non-Kerr object with different
spin. In this paper, I address the question whether measuring the Kerr spin
with both the continuum-fitting method and the K$\alpha$ iron line analysis of
the same object can be used to claim the Kerr nature of the black hole
candidate in the case of consistent results. The answer is more likely
negative: if the object is not a Kerr black hole but we assume it is, the two
techniques may anyway provide a very similar result.
Gas rotation in galaxy clusters: signatures and detectability in X-rays. (arXiv:1305.5519v1 [astro-ph.CO])
Gas rotation in galaxy clusters: signatures and detectability in X-rays. (arXiv:1305.5519v1 [astro-ph.CO]):
We study simple models of massive galaxy clusters in which the intracluster
medium (ICM) rotates differentially in equilibrium in the cluster gravitational
potential. We obtain the X-ray surface brightness maps, evaluating the isophote
flattening due to the gas rotation. Using a set of different rotation laws, we
put constraint on the amplitude of the rotation velocity, finding that rotation
curves with peak velocity up to \sim 600 km s^-1 are consistent with the
ellipticity profiles of observed clusters. We convolve each of our models with
the instrument response of the X-ray Calorimeter Spectrometer on board the
ASTRO-H to calculate the simulated X-ray spectra at different distance from the
X-ray centre. We demonstrate that such an instrument will allow us to measure
rotation of the ICM in massive clusters, even with rotation velocities as low
as \sim 100 km s^-1
We study simple models of massive galaxy clusters in which the intracluster
medium (ICM) rotates differentially in equilibrium in the cluster gravitational
potential. We obtain the X-ray surface brightness maps, evaluating the isophote
flattening due to the gas rotation. Using a set of different rotation laws, we
put constraint on the amplitude of the rotation velocity, finding that rotation
curves with peak velocity up to \sim 600 km s^-1 are consistent with the
ellipticity profiles of observed clusters. We convolve each of our models with
the instrument response of the X-ray Calorimeter Spectrometer on board the
ASTRO-H to calculate the simulated X-ray spectra at different distance from the
X-ray centre. We demonstrate that such an instrument will allow us to measure
rotation of the ICM in massive clusters, even with rotation velocities as low
as \sim 100 km s^-1
Non-parametric method for measuring gas inhomogeneities from X-ray observations of galaxy clusters. (arXiv:1305.5256v1 [astro-ph.CO])
Non-parametric method for measuring gas inhomogeneities from X-ray observations of galaxy clusters. (arXiv:1305.5256v1 [astro-ph.CO]):
We present a non-parametric method to measure inhomogeneities in the
intracluster medium (ICM) from X-ray observations of galaxy clusters. Analyzing
mock Chandra X-ray observations of simulated clusters, we show that our new
method enables the accurate recovery of the 3D gas density and gas clumping
factor profiles out to large radii of galaxy clusters. We then apply this
method to Chandra X-ray observations of Abell 1835 and present the first
determination of the gas clumping factor from the X-ray cluster data. We find
that the gas clumping factor in Abell 1835 increases with radius and reaches
~2-3 at r=R_{200}. This is in good agreement with the predictions of
hydrodynamical simulations, but it is significantly below the values inferred
from recent Suzaku observations. We further show that the radially increasing
gas clumping factor causes flattening of the derived entropy profile of the ICM
and affects physical interpretation of the cluster gas structure, especially at
the large cluster-centric radii. Our new technique should using for improving
our understanding of the cluster structure and to advance the use of galaxy
clusters as cosmological probes, by helping to exploit rich datasets provided
by Chandra and XMM-Newton X-ray space telescopes.
We present a non-parametric method to measure inhomogeneities in the
intracluster medium (ICM) from X-ray observations of galaxy clusters. Analyzing
mock Chandra X-ray observations of simulated clusters, we show that our new
method enables the accurate recovery of the 3D gas density and gas clumping
factor profiles out to large radii of galaxy clusters. We then apply this
method to Chandra X-ray observations of Abell 1835 and present the first
determination of the gas clumping factor from the X-ray cluster data. We find
that the gas clumping factor in Abell 1835 increases with radius and reaches
~2-3 at r=R_{200}. This is in good agreement with the predictions of
hydrodynamical simulations, but it is significantly below the values inferred
from recent Suzaku observations. We further show that the radially increasing
gas clumping factor causes flattening of the derived entropy profile of the ICM
and affects physical interpretation of the cluster gas structure, especially at
the large cluster-centric radii. Our new technique should using for improving
our understanding of the cluster structure and to advance the use of galaxy
clusters as cosmological probes, by helping to exploit rich datasets provided
by Chandra and XMM-Newton X-ray space telescopes.
Principal Component Analysis of Spectral Line Data: Analytic Formulation. (arXiv:1305.5071v1 [astro-ph.GA])
Principal Component Analysis of Spectral Line Data: Analytic Formulation. (arXiv:1305.5071v1 [astro-ph.GA]):
Principal component analysis is a powerful statistical system to investigate
the structure and dynamics of the molecular interstellar medium, with
particular emphasis on the study of turbulence, as revealed by spectroscopic
imaging of molecular line emission. To-date, the method to retrieve the power
law index of the velocity structure function or power spectrum has relied on an
empirical calibration and testing with model turbulent velocity fields, while
lacking a firm theoretical basis. In this paper, we present an analytic
formulation that reveals the detailed mechanics of the method and confirms
previous empirical calibrations of its recovery of the scale dependence of
turbulent velocity fluctuations.
Principal component analysis is a powerful statistical system to investigate
the structure and dynamics of the molecular interstellar medium, with
particular emphasis on the study of turbulence, as revealed by spectroscopic
imaging of molecular line emission. To-date, the method to retrieve the power
law index of the velocity structure function or power spectrum has relied on an
empirical calibration and testing with model turbulent velocity fields, while
lacking a firm theoretical basis. In this paper, we present an analytic
formulation that reveals the detailed mechanics of the method and confirms
previous empirical calibrations of its recovery of the scale dependence of
turbulent velocity fluctuations.
Unveiling the corona of the Milky Way via ram-pressure stripping of dwarf satellites. (arXiv:1305.4176v1 [astro-ph.GA])
Unveiling the corona of the Milky Way via ram-pressure stripping of dwarf satellites. (arXiv:1305.4176v1 [astro-ph.GA]):
The spatial segregation between dSphs and dIrrs in the Local Group has long
been regarded as evidence of an interaction with their host galaxies. In this
paper, we assume that ram-pressure stripping is the dominant mechanism that
removed gas from the dSphs and we use this to derive a lower bound on the
density of the corona of the Milky Way at large distances (50-90 kpc) from the
Galactic centre. At the same time, we derive an upper bound by demanding that
the interstellar medium of the dSphs is in pressure equilibrium with the hot
corona. We consider two dwarfs (Sextans and Carina) with well-determined orbits
and star formation histories. Our approach introduces several novel features:
we use the measured star formation histories of the dwarfs to derive the time
at which they last lost their gas, and (via a modified version of the
Kennicutt-Schmidt relation) their internal gas density at that time; we use a
large suite of 2D hydrodynamical simulations to model the gas stripping; and we
include supernova feedback tied to the gas content. Despite having very
different orbits and star formation histories, we find results for the two
dSphs that are in excellent agreement with one another. We derive an average
particle density of the corona of the Milky Way at 50-90 kpc in the range
1.3-3.6 10^{-4} cm^{-3}. Including additional constraints from X-ray emission
limits and pulsar dispersion measurements, we extrapolate Galactic coronal
density profiles and we estimate the fraction of baryons that can exist within
the virial radius of the Milky Way. For an isothermal corona (T=1.8 10^6 K)
this is small, 10-20 % of the universal baryon fraction. Only a hot (T=3 10^6
K) and adiabatic corona can contain all of the Galaxy's missing baryons. Models
for the Milky Way must explain why its corona is in a hot adiabatic thermal
state or why a large fraction of its baryons lie beyond the virial radius.
The spatial segregation between dSphs and dIrrs in the Local Group has long
been regarded as evidence of an interaction with their host galaxies. In this
paper, we assume that ram-pressure stripping is the dominant mechanism that
removed gas from the dSphs and we use this to derive a lower bound on the
density of the corona of the Milky Way at large distances (50-90 kpc) from the
Galactic centre. At the same time, we derive an upper bound by demanding that
the interstellar medium of the dSphs is in pressure equilibrium with the hot
corona. We consider two dwarfs (Sextans and Carina) with well-determined orbits
and star formation histories. Our approach introduces several novel features:
we use the measured star formation histories of the dwarfs to derive the time
at which they last lost their gas, and (via a modified version of the
Kennicutt-Schmidt relation) their internal gas density at that time; we use a
large suite of 2D hydrodynamical simulations to model the gas stripping; and we
include supernova feedback tied to the gas content. Despite having very
different orbits and star formation histories, we find results for the two
dSphs that are in excellent agreement with one another. We derive an average
particle density of the corona of the Milky Way at 50-90 kpc in the range
1.3-3.6 10^{-4} cm^{-3}. Including additional constraints from X-ray emission
limits and pulsar dispersion measurements, we extrapolate Galactic coronal
density profiles and we estimate the fraction of baryons that can exist within
the virial radius of the Milky Way. For an isothermal corona (T=1.8 10^6 K)
this is small, 10-20 % of the universal baryon fraction. Only a hot (T=3 10^6
K) and adiabatic corona can contain all of the Galaxy's missing baryons. Models
for the Milky Way must explain why its corona is in a hot adiabatic thermal
state or why a large fraction of its baryons lie beyond the virial radius.
Summary of the 2013 IACHEC Meeting. (arXiv:1305.4480v1 [astro-ph.IM])
Summary of the 2013 IACHEC Meeting. (arXiv:1305.4480v1 [astro-ph.IM]):
We present the main results of the 8th International Astronomical Consortium
for High Energy Calibration (IACHEC) meeting, held in Theddingworth,
Leicestershire, between March 25 and 28, 2013. Over 50 scientists directly
involved in the calibration of operational and future high-energy missions
gathered during 3.5 days to discuss the status of the X-ray payload
inter-calibration, as well as possible ways to improve it. Sect. 4 of this
Report summarises our current understanding of the energy-dependent
inter-calibration status.
We present the main results of the 8th International Astronomical Consortium
for High Energy Calibration (IACHEC) meeting, held in Theddingworth,
Leicestershire, between March 25 and 28, 2013. Over 50 scientists directly
involved in the calibration of operational and future high-energy missions
gathered during 3.5 days to discuss the status of the X-ray payload
inter-calibration, as well as possible ways to improve it. Sect. 4 of this
Report summarises our current understanding of the energy-dependent
inter-calibration status.
Asymmetric Ejecta Distribution in SN 1006. (arXiv:1305.4489v1 [astro-ph.HE])
Asymmetric Ejecta Distribution in SN 1006. (arXiv:1305.4489v1 [astro-ph.HE]):
We present the results from deep X-ray observations (~400 ks in total) of SN
1006 by the X-ray astronomy satellite Suzaku. The thermal spectrum from the
entire supernova remnant (SNR) exhibits prominent emission lines of O, Ne, Mg,
Si, S, Ar, Ca, and Fe. The observed abundance pattern in the ejecta components
is in good agreement with that predicted by a standard model of Type Ia
supernovae (SNe). The spatially resolved analysis reveals that the distribution
of the O-burning and incomplete Si-burning products (Si, S, and Ar) is
asymmetric, while that of the C-burning products (O, Ne, and Mg) is relatively
uniform in the SNR interior. The peak position of the former is clearly shifted
by 5' (~3.2 pc at a distance of 2.2 kpc) to the southeast from the SNR's
geometric center. Using the SNR age of ~1000 yr, we constrain the velocity
asymmetry (in projection) of ejecta to be ~3100 km/s. The abundance of Fe is
also significantly higher in the southeast region than in the northwest region.
Given that the non-uniformity is observed only among the heavier elements (Si
through Fe), we argue that SN 1006 originates from an asymmetric explosion, as
is expected from recent multi-dimensional simulations of Type Ia SNe, although
we cannot eliminate the possibility that an inhomogeneous ambient medium
induced the apparent non-uniformity. Possible evidence for the Cr K-shell line
and line broadening in the Fe K-shell emission is also found.
We present the results from deep X-ray observations (~400 ks in total) of SN
1006 by the X-ray astronomy satellite Suzaku. The thermal spectrum from the
entire supernova remnant (SNR) exhibits prominent emission lines of O, Ne, Mg,
Si, S, Ar, Ca, and Fe. The observed abundance pattern in the ejecta components
is in good agreement with that predicted by a standard model of Type Ia
supernovae (SNe). The spatially resolved analysis reveals that the distribution
of the O-burning and incomplete Si-burning products (Si, S, and Ar) is
asymmetric, while that of the C-burning products (O, Ne, and Mg) is relatively
uniform in the SNR interior. The peak position of the former is clearly shifted
by 5' (~3.2 pc at a distance of 2.2 kpc) to the southeast from the SNR's
geometric center. Using the SNR age of ~1000 yr, we constrain the velocity
asymmetry (in projection) of ejecta to be ~3100 km/s. The abundance of Fe is
also significantly higher in the southeast region than in the northwest region.
Given that the non-uniformity is observed only among the heavier elements (Si
through Fe), we argue that SN 1006 originates from an asymmetric explosion, as
is expected from recent multi-dimensional simulations of Type Ia SNe, although
we cannot eliminate the possibility that an inhomogeneous ambient medium
induced the apparent non-uniformity. Possible evidence for the Cr K-shell line
and line broadening in the Fe K-shell emission is also found.
A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys. (arXiv:1305.3917v1 [astro-ph.HE])
A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys. (arXiv:1305.3917v1 [astro-ph.HE]):
We present an investigation into how well the properties of the accretion
flow onto a supermassive black hole may be coupled to those of the overlying
hot corona. To do so, we specifically measure the characteristic spectral
index, Gamma, of a power-law energy distribution, over an energy range of 2 to
10 keV, for X-ray selected, broad-lined radio-quiet AGN up to z~2 in COSMOS and
E-CDF-S. We test the previously reported dependence between Gamma and black
hole mass, FWHM and Eddington ratio using a sample of AGN covering a broad
range in these parameters based on both the Mg ii and H-alpha emission lines
with the later afforded by recent near infrared spectroscopic observations
using Subaru/FMOS. We calculate the Eddington ratios, lambda_Edd, for sources
where a bolometric luminosity (L_Bol) has been presented in the literature,
based on SED fitting, or, for sources where these data do not exist, we
calculate L_Bol using a bolometric correction to the LX, derived from a
relationship between the bolometric correction, and LX/L3000. From a sample of
69 X-ray bright sources (>250 counts), where Gamma can be measured with
greatest precision, with an estimate of L_Bol, we find a statistically
significant correlation between Gamma and lambda_Edd, which is highly
significant with a chance probability of 6.59x10^-8. A statistically
significant correlation between Gamma and the FWHM of the optical lines is
confirmed, but at lower significance than with lambda_Edd indicating that
lambda_Edd is the key parameter driving conditions in the corona. Linear
regression analysis reveals that Gamma=(0.32+/-0.05)log10
lambda_Edd+(2.27+/-0.06) and
Gamma=(-0.69+/-0.11)log10(FWHM/km/s)+(4.44+/-0.42). Our results on
Gamma-lambda_Edd are in very good agreement with previous results. (ABRIDGED)
We present an investigation into how well the properties of the accretion
flow onto a supermassive black hole may be coupled to those of the overlying
hot corona. To do so, we specifically measure the characteristic spectral
index, Gamma, of a power-law energy distribution, over an energy range of 2 to
10 keV, for X-ray selected, broad-lined radio-quiet AGN up to z~2 in COSMOS and
E-CDF-S. We test the previously reported dependence between Gamma and black
hole mass, FWHM and Eddington ratio using a sample of AGN covering a broad
range in these parameters based on both the Mg ii and H-alpha emission lines
with the later afforded by recent near infrared spectroscopic observations
using Subaru/FMOS. We calculate the Eddington ratios, lambda_Edd, for sources
where a bolometric luminosity (L_Bol) has been presented in the literature,
based on SED fitting, or, for sources where these data do not exist, we
calculate L_Bol using a bolometric correction to the LX, derived from a
relationship between the bolometric correction, and LX/L3000. From a sample of
69 X-ray bright sources (>250 counts), where Gamma can be measured with
greatest precision, with an estimate of L_Bol, we find a statistically
significant correlation between Gamma and lambda_Edd, which is highly
significant with a chance probability of 6.59x10^-8. A statistically
significant correlation between Gamma and the FWHM of the optical lines is
confirmed, but at lower significance than with lambda_Edd indicating that
lambda_Edd is the key parameter driving conditions in the corona. Linear
regression analysis reveals that Gamma=(0.32+/-0.05)log10
lambda_Edd+(2.27+/-0.06) and
Gamma=(-0.69+/-0.11)log10(FWHM/km/s)+(4.44+/-0.42). Our results on
Gamma-lambda_Edd are in very good agreement with previous results. (ABRIDGED)
Searching for a 0.1-1 keV Cosmic Axion Background. (arXiv:1305.3603v1 [astro-ph.CO])
Searching for a 0.1-1 keV Cosmic Axion Background. (arXiv:1305.3603v1 [astro-ph.CO]):
Primordial decays of string theory moduli at z \sim 10^{12} naturally
generate a dark radiation Cosmic Axion Background (CAB) with 0.1 - 1 keV
energies. This CAB can be detected through axion-photon conversion in
astrophysical magnetic fields to give quasi-thermal excesses in the extreme
ultraviolet and soft X-ray bands. Substantial and observable luminosities may
be generated even for axion-photon couplings \ll 10^{-11} GeV^{-1}. We propose
that axion-photon conversion may explain the observed excess emission of soft
X-rays from galaxy clusters, and may also contribute to the diffuse unresolved
cosmic X-ray background. We list a number of correlated predictions of the
scenario.
Primordial decays of string theory moduli at z \sim 10^{12} naturally
generate a dark radiation Cosmic Axion Background (CAB) with 0.1 - 1 keV
energies. This CAB can be detected through axion-photon conversion in
astrophysical magnetic fields to give quasi-thermal excesses in the extreme
ultraviolet and soft X-ray bands. Substantial and observable luminosities may
be generated even for axion-photon couplings \ll 10^{-11} GeV^{-1}. We propose
that axion-photon conversion may explain the observed excess emission of soft
X-rays from galaxy clusters, and may also contribute to the diffuse unresolved
cosmic X-ray background. We list a number of correlated predictions of the
scenario.
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