XMM-Newton evidence of shocked ISM in SN 1006: indications of hadronic acceleration. (arXiv:1208.5966v1 [astro-ph.HE]):
Shock fronts in young supernova remnants are the best candidates for being
sites of cosmic ray acceleration up to a few PeV, though conclusive
experimental evidence is still lacking. Hadron acceleration is expected to
increase the shock compression ratio, providing higher postshock densities, but
X-ray emission from shocked ambient medium has not firmly been detected yet in
remnants where particle acceleration is at work. We exploited the deep
observations of the XMM-Newton Large Program on SN 1006 to verify this
prediction. We performed spatially resolved spectral analysis of a set of
regions covering the southeastern rim of SN 1006. We studied the spatial
distribution of the thermodynamic properties of the ambient medium and
carefully verified the robustness of the result with respect to the analysis
method. We detected the contribution of the shocked ambient medium. We also
found that the postshock density of the interstellar medium significantly
increases in regions where particle acceleration is efficient. Under the
assumption of uniform preshock density, we found that the shock compression
ratio reaches a value of ~6 in regions near the nonthermal limbs. Our results
support the predictions of shock modification theory and indicate that effects
of acceleration of cosmic ray hadrons on the postshock plasma can be observed
in supernova remnants.
Thursday, August 30, 2012
Galaxy cluster outskirts: a universal entropy profile for relaxed clusters?. (arXiv:1208.5950v1 [astro-ph.CO])
Galaxy cluster outskirts: a universal entropy profile for relaxed clusters?. (arXiv:1208.5950v1 [astro-ph.CO]):
We fit a functional form for a universal ICM entropy profile to the scaled
entropy profiles of a catalogue of X-ray galaxy cluster outskirts results,
which are all relaxed cool core clusters at redshift below 0.25. We also
investigate the functional form suggested by Lapi et al. and Cavaliere et al.
for the behaviour of the entropy profile in the outskirts and find it to fit
the data well outside 0.3r200 . We highlight the discrepancy in the entropy
profile behaviour in the outskirts between observations and the numerical
simulations of Burns et al., and show that the entropy profile flattening due
to gas clumping calculated by Nagai & Lau is insufficient to match
observations, suggesting that gas clumping alone cannot be responsible for all
of the entropy profile flattening in the cluster outskirts. The entropy
profiles found with Suzaku are found to be consistent with ROSAT, XMM-Newton
and Planck results.
We fit a functional form for a universal ICM entropy profile to the scaled
entropy profiles of a catalogue of X-ray galaxy cluster outskirts results,
which are all relaxed cool core clusters at redshift below 0.25. We also
investigate the functional form suggested by Lapi et al. and Cavaliere et al.
for the behaviour of the entropy profile in the outskirts and find it to fit
the data well outside 0.3r200 . We highlight the discrepancy in the entropy
profile behaviour in the outskirts between observations and the numerical
simulations of Burns et al., and show that the entropy profile flattening due
to gas clumping calculated by Nagai & Lau is insufficient to match
observations, suggesting that gas clumping alone cannot be responsible for all
of the entropy profile flattening in the cluster outskirts. The entropy
profiles found with Suzaku are found to be consistent with ROSAT, XMM-Newton
and Planck results.
Planck intermediate results. VIII. Filaments between interacting clusters. (arXiv:1208.5911v1 [astro-ph.CO])
Planck intermediate results. VIII. Filaments between interacting clusters. (arXiv:1208.5911v1 [astro-ph.CO]):
About half of the baryons of the Universe are expected to be in the form of
filaments of hot and low density intergalactic medium. Most of these baryons
remain undetected even by the most advanced X-ray observatories which are
limited in sensitivity to the diffuse low density medium. The Planck satellite
has provided hundreds of detections of the hot gas in clusters of galaxies via
the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for
studying extended low density media through the tSZ effect. In this paper we
use the Planck data to search for signatures of a fraction of these missing
baryons between pairs of galaxy clusters. Cluster pairs are good candidates for
searching for the hotter and denser phase of the intergalactic medium (which is
more easily observed through the SZ effect). Using an X-ray catalogue of
clusters and the Planck data, we select physical pairs of clusters as
candidates. Using the Planck data we construct a local map of the tSZ effect
centered on each pair of galaxy clusters. ROSAT data is used to construct X-ray
maps of these pairs. After having modelled and subtracted the tSZ effect and
X-ray emission for each cluster in the pair we study the residuals on both the
SZ and X-ray maps. For the merging cluster pair A399-A401 we observe a
significant tSZ effect signal in the intercluster region beyond the virial
radii of the clusters. A joint X-ray SZ analysis allows us to constrain the
temperature and density of this intercluster medium. We obtain a temperature of
kT = 7.1 +- 0.9, keV (consistent with previous estimates) and a baryon density
of (3.7 +- 0.2)x10^-4, cm^-3. The Planck satellite mission has provided the
first SZ detection of the hot and diffuse intercluster gas.
About half of the baryons of the Universe are expected to be in the form of
filaments of hot and low density intergalactic medium. Most of these baryons
remain undetected even by the most advanced X-ray observatories which are
limited in sensitivity to the diffuse low density medium. The Planck satellite
has provided hundreds of detections of the hot gas in clusters of galaxies via
the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for
studying extended low density media through the tSZ effect. In this paper we
use the Planck data to search for signatures of a fraction of these missing
baryons between pairs of galaxy clusters. Cluster pairs are good candidates for
searching for the hotter and denser phase of the intergalactic medium (which is
more easily observed through the SZ effect). Using an X-ray catalogue of
clusters and the Planck data, we select physical pairs of clusters as
candidates. Using the Planck data we construct a local map of the tSZ effect
centered on each pair of galaxy clusters. ROSAT data is used to construct X-ray
maps of these pairs. After having modelled and subtracted the tSZ effect and
X-ray emission for each cluster in the pair we study the residuals on both the
SZ and X-ray maps. For the merging cluster pair A399-A401 we observe a
significant tSZ effect signal in the intercluster region beyond the virial
radii of the clusters. A joint X-ray SZ analysis allows us to constrain the
temperature and density of this intercluster medium. We obtain a temperature of
kT = 7.1 +- 0.9, keV (consistent with previous estimates) and a baryon density
of (3.7 +- 0.2)x10^-4, cm^-3. The Planck satellite mission has provided the
first SZ detection of the hot and diffuse intercluster gas.
Long XMM observation of the Narrow-Line Seyfert 1 galaxy IRAS13224-3809: rapid variability, high spin and a soft lag. (arXiv:1208.5898v1 [astro-ph.HE])
Long XMM observation of the Narrow-Line Seyfert 1 galaxy IRAS13224-3809: rapid variability, high spin and a soft lag. (arXiv:1208.5898v1 [astro-ph.HE]):
Results are presented from a 500ks long XMM-Newton observation of the
Narrow-Line Seyfert 1 galaxy IRAS13224-3809. The source is rapidly variable on
timescales down to a few 100s. The spectrum shows strong broad Fe-K and L
emission features which are interpreted as arising from reflection from the
inner parts of an accretion disc around a rapidly spinning black hole. Assuming
a power-law emissivity for the reflected flux and that the innermost radius
corresponds to the innermost stable circular orbit, the black hole spin is
measured to be 0.988 with a statistical precision better than one per cent.
Systematic uncertainties are discussed. A soft X-ray lag of 100s confirms this
scenario. The bulk of the power-law continuum source is located at a radius of
2-3 gravitational radii.
Results are presented from a 500ks long XMM-Newton observation of the
Narrow-Line Seyfert 1 galaxy IRAS13224-3809. The source is rapidly variable on
timescales down to a few 100s. The spectrum shows strong broad Fe-K and L
emission features which are interpreted as arising from reflection from the
inner parts of an accretion disc around a rapidly spinning black hole. Assuming
a power-law emissivity for the reflected flux and that the innermost radius
corresponds to the innermost stable circular orbit, the black hole spin is
measured to be 0.988 with a statistical precision better than one per cent.
Systematic uncertainties are discussed. A soft X-ray lag of 100s confirms this
scenario. The bulk of the power-law continuum source is located at a radius of
2-3 gravitational radii.
The Black Hole Remnant of Black Hole-Neutron Star Coalescing Binaries. (arXiv:1208.5869v1 [gr-qc])
The Black Hole Remnant of Black Hole-Neutron Star Coalescing Binaries. (arXiv:1208.5869v1 [gr-qc]):
We present a model for determining the dimensionless spin parameter and mass
of the black hole remnant of black hole-neutron star mergers with parallel
orbital angular momentum and initial black hole spin. This approach is based on
the Buonanno, Kidder, and Lehner method for binary black holes and it is
successfully tested against the results of numerical-relativity simulations:
the dimensionless spin parameter is predicted with absolute error $\lesssim
0.02$, whereas the relative error on the final mass is $\lesssim 2$%, its
distribution being pronouncedly peaked at 1%. Our approach and the fit to the
torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use
analytical model that accurately describes the remnant of BH-NS mergers. We
investigate the space of parameters consisting of the binary mass ratio, the
initial black hole spin, and the neutron star mass and equation of state. We
provide indirect support to the cosmic censorship conjecture for black hole
remnants of black hole-neutron star mergers. We show that the presence of a
neutron star affects the quasi-normal mode frequency of the black hole remnant,
thus suggesting that the ringdown epoch of the gravitational wave signal may
virtually be used to (1) distinguish binary black hole from black hole-neutron
star mergers and to (2) constrain the neutron star equation of state.
We present a model for determining the dimensionless spin parameter and mass
of the black hole remnant of black hole-neutron star mergers with parallel
orbital angular momentum and initial black hole spin. This approach is based on
the Buonanno, Kidder, and Lehner method for binary black holes and it is
successfully tested against the results of numerical-relativity simulations:
the dimensionless spin parameter is predicted with absolute error $\lesssim
0.02$, whereas the relative error on the final mass is $\lesssim 2$%, its
distribution being pronouncedly peaked at 1%. Our approach and the fit to the
torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use
analytical model that accurately describes the remnant of BH-NS mergers. We
investigate the space of parameters consisting of the binary mass ratio, the
initial black hole spin, and the neutron star mass and equation of state. We
provide indirect support to the cosmic censorship conjecture for black hole
remnants of black hole-neutron star mergers. We show that the presence of a
neutron star affects the quasi-normal mode frequency of the black hole remnant,
thus suggesting that the ringdown epoch of the gravitational wave signal may
virtually be used to (1) distinguish binary black hole from black hole-neutron
star mergers and to (2) constrain the neutron star equation of state.
How Baryonic Processes affect Strong Lensing properties of Simulated Galaxy Clusters. (arXiv:1208.5770v1 [astro-ph.CO])
How Baryonic Processes affect Strong Lensing properties of Simulated Galaxy Clusters. (arXiv:1208.5770v1 [astro-ph.CO]):
The observed abundance of giant arcs produced by galaxy cluster lenses and
the measured Einstein radii have presented a source of tension for LCDM.
Previous cosmological tests for high-redshift clusters (z>0.5) have suffered
from small number statistics in the simulated sample and the implementation of
baryonic physics is likely to affect the outcome. We analyse zoomed-in
simulations of a fairly large sample of cluster-sized objects, with Mvir >
3x10^14 Msun/h, identified at z=0.25 and z=0.5, for a concordance LCDM
cosmology. We start with dark matter only simulations, and then add gas
hydrodynamics, with different treatments of baryonic processes: non-radiative
cooling, radiative cooling with star formation and galactic winds powered by
supernova explosions, and finally including the effect of AGN feedback. We find
that the addition of gas in non-radiative simulations does not change the
strong lensing predictions significantly, but gas cooling and star formation
together significantly increase the number of expected giant arcs and the
Einstein radii, particularly for lower redshift clusters and lower source
redshifts. Further inclusion of AGN feedback reduces the predicted strong
lensing efficiencies such that the lensing probability distributions becomes
closer to those obtained for simulations including only dark matter. Our
results indicate that the inclusion of baryonic physics in simulations will not
solve the arc-statistics problem at low redshifts, when the physical processes
included provide a realistic description of cooling in the central regions of
galaxy clusters. [Abridged]
The observed abundance of giant arcs produced by galaxy cluster lenses and
the measured Einstein radii have presented a source of tension for LCDM.
Previous cosmological tests for high-redshift clusters (z>0.5) have suffered
from small number statistics in the simulated sample and the implementation of
baryonic physics is likely to affect the outcome. We analyse zoomed-in
simulations of a fairly large sample of cluster-sized objects, with Mvir >
3x10^14 Msun/h, identified at z=0.25 and z=0.5, for a concordance LCDM
cosmology. We start with dark matter only simulations, and then add gas
hydrodynamics, with different treatments of baryonic processes: non-radiative
cooling, radiative cooling with star formation and galactic winds powered by
supernova explosions, and finally including the effect of AGN feedback. We find
that the addition of gas in non-radiative simulations does not change the
strong lensing predictions significantly, but gas cooling and star formation
together significantly increase the number of expected giant arcs and the
Einstein radii, particularly for lower redshift clusters and lower source
redshifts. Further inclusion of AGN feedback reduces the predicted strong
lensing efficiencies such that the lensing probability distributions becomes
closer to those obtained for simulations including only dark matter. Our
results indicate that the inclusion of baryonic physics in simulations will not
solve the arc-statistics problem at low redshifts, when the physical processes
included provide a realistic description of cooling in the central regions of
galaxy clusters. [Abridged]
Wednesday, August 29, 2012
Constraining the Vela Pulsar's Radio Emission Region Using Nyquist-Limited Scintillation Statistics. (arXiv:1208.5485v1 [astro-ph.SR])
Constraining the Vela Pulsar's Radio Emission Region Using Nyquist-Limited Scintillation Statistics. (arXiv:1208.5485v1 [astro-ph.SR]):
Using a novel technique, we achieve ~100 picoarcsecond resolution and set an
upper bound of less than 4 km for the characteristic size of the Vela pulsar's
emission region. Specifically, we analyze flux-density statistics of the Vela
pulsar at 760 MHz. Because the pulsar exhibits strong diffractive
scintillation, these statistics convey information about the spatial extent of
the radio emission region. We measure both a characteristic size of the
emission region and the emission sizes for individual pulses. Our results imply
that the radio emission altitude for the Vela pulsar at this frequency is less
than 340 km.
Using a novel technique, we achieve ~100 picoarcsecond resolution and set an
upper bound of less than 4 km for the characteristic size of the Vela pulsar's
emission region. Specifically, we analyze flux-density statistics of the Vela
pulsar at 760 MHz. Because the pulsar exhibits strong diffractive
scintillation, these statistics convey information about the spatial extent of
the radio emission region. We measure both a characteristic size of the
emission region and the emission sizes for individual pulses. Our results imply
that the radio emission altitude for the Vela pulsar at this frequency is less
than 340 km.
The importance of cooling in triggering the collapse of hypermassive neutron stars. (arXiv:1208.5487v1 [astro-ph.HE])
The importance of cooling in triggering the collapse of hypermassive neutron stars. (arXiv:1208.5487v1 [astro-ph.HE]):
The inspiral and merger of a binary neutron star (NSNS) can lead to the
formation of a hypermassive neutron star (HMNS). As the HMNS loses thermal
pressure due to neutrino cooling and/or centrifugal support due to
gravitational wave (GW) emission, and/or magnetic breaking of differential
rotation it will collapse to a black hole. To assess the importance of
shock-induced thermal pressure and cooling, we adopt an idealized equation of
state and perform NSNS simulations in full GR through late inspiral, merger,
and HMNS formation, accounting for cooling. We show that thermal pressure
contributes significantly to the support of the HMNS against collapse and that
thermal cooling accelerates its "delayed" collapse. Our simulations demonstrate
explicitly that cooling can induce the catastrophic collapse of a hot
hypermassive neutron star formed following the merger of binary neutron stars.
Thus, cooling physics is important to include in NSNS merger calculations to
accurately determine the lifetime of the HMNS remnant and to extract
information about the NS equation of state, cooling mechanisms, bar
instabilities and B-fields from the GWs emitted during the transient phase
prior to BH formation.
The inspiral and merger of a binary neutron star (NSNS) can lead to the
formation of a hypermassive neutron star (HMNS). As the HMNS loses thermal
pressure due to neutrino cooling and/or centrifugal support due to
gravitational wave (GW) emission, and/or magnetic breaking of differential
rotation it will collapse to a black hole. To assess the importance of
shock-induced thermal pressure and cooling, we adopt an idealized equation of
state and perform NSNS simulations in full GR through late inspiral, merger,
and HMNS formation, accounting for cooling. We show that thermal pressure
contributes significantly to the support of the HMNS against collapse and that
thermal cooling accelerates its "delayed" collapse. Our simulations demonstrate
explicitly that cooling can induce the catastrophic collapse of a hot
hypermassive neutron star formed following the merger of binary neutron stars.
Thus, cooling physics is important to include in NSNS merger calculations to
accurately determine the lifetime of the HMNS remnant and to extract
information about the NS equation of state, cooling mechanisms, bar
instabilities and B-fields from the GWs emitted during the transient phase
prior to BH formation.
Planck Intermediate Results. IX. Detection of the Galactic haze with Planck. (arXiv:1208.5483v1 [astro-ph.GA])
Planck Intermediate Results. IX. Detection of the Galactic haze with Planck. (arXiv:1208.5483v1 [astro-ph.GA]):
Using precise full-sky observations from Planck, and applying several methods
of component separation, we identify and characterize the emission from the
Galactic "haze" at microwave wavelengths. The haze is a distinct component of
diffuse Galactic emission, roughly centered on the Galactic centre, and extends
to |b| ~35 deg in Galactic latitude and |l| ~15 deg in longitude. By combining
the Planck data with observations from the WMAP we are able to determine the
spectrum of this emission to high accuracy, unhindered by the large systematic
biases present in previous analyses. The derived spectrum is consistent with
power-law emission with a spectral index of -2.55 +/- 0.05, thus excluding
free-free emission as the source and instead favouring hard-spectrum
synchrotron radiation from an electron population with a spectrum (number
density per energy) dN/dE ~ E^-2.1. At Galactic latitudes |b|<30 deg, the
microwave haze morphology is consistent with that of the Fermi gamma-ray "haze"
or "bubbles," indicating that we have a multi-wavelength view of a distinct
component of our Galaxy. Given both the very hard spectrum and the extended
nature of the emission, it is highly unlikely that the haze electrons result
from supernova shocks in the Galactic disk. Instead, a new mechanism for
cosmic-ray acceleration in the centre of our Galaxy is implied.
Using precise full-sky observations from Planck, and applying several methods
of component separation, we identify and characterize the emission from the
Galactic "haze" at microwave wavelengths. The haze is a distinct component of
diffuse Galactic emission, roughly centered on the Galactic centre, and extends
to |b| ~35 deg in Galactic latitude and |l| ~15 deg in longitude. By combining
the Planck data with observations from the WMAP we are able to determine the
spectrum of this emission to high accuracy, unhindered by the large systematic
biases present in previous analyses. The derived spectrum is consistent with
power-law emission with a spectral index of -2.55 +/- 0.05, thus excluding
free-free emission as the source and instead favouring hard-spectrum
synchrotron radiation from an electron population with a spectrum (number
density per energy) dN/dE ~ E^-2.1. At Galactic latitudes |b|<30 deg, the
microwave haze morphology is consistent with that of the Fermi gamma-ray "haze"
or "bubbles," indicating that we have a multi-wavelength view of a distinct
component of our Galaxy. Given both the very hard spectrum and the extended
nature of the emission, it is highly unlikely that the haze electrons result
from supernova shocks in the Galactic disk. Instead, a new mechanism for
cosmic-ray acceleration in the centre of our Galaxy is implied.
Tuesday, August 28, 2012
X-ray evidence for ultra-fast outflows in local AGNs. (arXiv:1208.5031v1 [astro-ph.HE])
X-ray evidence for ultra-fast outflows in local AGNs. (arXiv:1208.5031v1 [astro-ph.HE]):
X-ray evidence for ultra-fast outflows (UFOs) has been recently reported in a
number of local AGNs through the detection of blue-shifted Fe XXV/XXVI
absorption lines. We present the results of a comprehensive spectral analysis
of a large sample of 42 local Seyferts and 5 Broad-Line Radio Galaxies (BLRGs)
observed with XMM-Newton and Suzaku. We detect UFOs in >40% of the sources.
Their outflow velocities are in the range 0.03-0.3c, with a mean value of
~0.14c. The ionization is high, in the range logxi~3-6 erg s^{-1} cm, and also
the associated column densities are large, in the interval ~10^{22}-10^{24}
cm^{-2}. Overall, these results point to the presence of highly ionized and
massive outflowing material in the innermost regions of AGNs. Their variability
and location on sub-pc scales favor a direct association with accretion disk
winds/outflows. This also suggests that UFOs may potentially play a significant
role in the AGN cosmological feedback besides jets and their study can provide
important clues on the connection between accretion disks, winds and jets.
X-ray evidence for ultra-fast outflows (UFOs) has been recently reported in a
number of local AGNs through the detection of blue-shifted Fe XXV/XXVI
absorption lines. We present the results of a comprehensive spectral analysis
of a large sample of 42 local Seyferts and 5 Broad-Line Radio Galaxies (BLRGs)
observed with XMM-Newton and Suzaku. We detect UFOs in >40% of the sources.
Their outflow velocities are in the range 0.03-0.3c, with a mean value of
~0.14c. The ionization is high, in the range logxi~3-6 erg s^{-1} cm, and also
the associated column densities are large, in the interval ~10^{22}-10^{24}
cm^{-2}. Overall, these results point to the presence of highly ionized and
massive outflowing material in the innermost regions of AGNs. Their variability
and location on sub-pc scales favor a direct association with accretion disk
winds/outflows. This also suggests that UFOs may potentially play a significant
role in the AGN cosmological feedback besides jets and their study can provide
important clues on the connection between accretion disks, winds and jets.
Absorption Features in the X-ray Spectrum of an Ordinary Radio Pulsar. (arXiv:1208.5400v1 [astro-ph.HE])
Absorption Features in the X-ray Spectrum of an Ordinary Radio Pulsar. (arXiv:1208.5400v1 [astro-ph.HE]):
The vast majority of known non-accreting neutron stars (NSs) are
rotation-powered radio and/or gamma-ray pulsars. So far, their multiwavelength
spectra have all been described satisfactorily by thermal and non-thermal
continuum models, with no spectral lines. Spectral features have, however, been
found in a handful of exotic NSs and thought to be a manifestation of their
unique traits. Here we report the detection of absorption features in the X-ray
spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings
bridge the gap between the spectra of pulsars and other, more exotic, NSs,
suggesting that the features are more common in the NS spectra than they have
been thought so far.
The vast majority of known non-accreting neutron stars (NSs) are
rotation-powered radio and/or gamma-ray pulsars. So far, their multiwavelength
spectra have all been described satisfactorily by thermal and non-thermal
continuum models, with no spectral lines. Spectral features have, however, been
found in a handful of exotic NSs and thought to be a manifestation of their
unique traits. Here we report the detection of absorption features in the X-ray
spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings
bridge the gap between the spectra of pulsars and other, more exotic, NSs,
suggesting that the features are more common in the NS spectra than they have
been thought so far.
Dynamical Capture Binary Neutron Star Mergers. (arXiv:1208.5279v1 [astro-ph.HE])
Dynamical Capture Binary Neutron Star Mergers. (arXiv:1208.5279v1 [astro-ph.HE]):
We study dynamical capture, binary neutron star mergers as may arise in dense
stellar regions such as globular clusters. Using general-relativistic
hydrodynamics we find that these mergers can result in the prompt collapse to a
black hole or in the formation of a hypermassive neutron star, depending not
only on the neutron star equation of state, but also on impact parameter. We
also find that these mergers can produce accretion disks of up to a tenth of a
solar mass, and unbound ejected material of up to a few percent of a solar
mass. We comment on the gravitational radiation and electromagnetic transients
that these sources may produce.
We study dynamical capture, binary neutron star mergers as may arise in dense
stellar regions such as globular clusters. Using general-relativistic
hydrodynamics we find that these mergers can result in the prompt collapse to a
black hole or in the formation of a hypermassive neutron star, depending not
only on the neutron star equation of state, but also on impact parameter. We
also find that these mergers can produce accretion disks of up to a tenth of a
solar mass, and unbound ejected material of up to a few percent of a solar
mass. We comment on the gravitational radiation and electromagnetic transients
that these sources may produce.
The typical mass ratio and typical final spin in supermassive black hole mergers. (arXiv:1208.5251v1 [gr-qc])
The typical mass ratio and typical final spin in supermassive black hole mergers. (arXiv:1208.5251v1 [gr-qc]):
We prove that merging supermassive black holes (SMBHs) typically have neither
equal masses, nor is their mass ratio too extreme. The majority of such mergers
fall into the mass ratio range of 1:30 to 1:3, implying a spin flip during the
inspiral. We also present a simple expression for the final spin $\chi_{f}$ of
the emerging SMBH, as function of the mass ratio, initial spin magnitudes, and
orientation of the spins with respect to the orbital plane and each other. This
formula approximates well more cumbersome expressions obtained from the fit
with numerical simulations. By integrating over all equally likely orientations
for precessing mergers we determine a lower approximant to the final spin
distribution as function of the mass ratio alone. By folding this with the
derived mass ratio dependent merger rate we derive a lower bound to the typical
final spin value after mergers. We repeat the procedure deriving an upper bound
for the typical spin in the case when the spins are aligned to the orbital
angular momentum, such that there is no precession in the system. Both slopes
of $\chi_{f}$ as function of the initial spins being smaller than one lead to
two attractors at $\chi_{f}^{prec}=0.2$ and $\chi_{f}^{align}=0.45$,
respectively. Real mergers, biased toward partial alignment by interactions
with the environment (accretion, host galaxy, etc.) would generate a typical
final spin lying between these two limiting values. These are the typical
values of the spin after the merger, starting from which the spin can built up
by further gaseous accretion.
We prove that merging supermassive black holes (SMBHs) typically have neither
equal masses, nor is their mass ratio too extreme. The majority of such mergers
fall into the mass ratio range of 1:30 to 1:3, implying a spin flip during the
inspiral. We also present a simple expression for the final spin $\chi_{f}$ of
the emerging SMBH, as function of the mass ratio, initial spin magnitudes, and
orientation of the spins with respect to the orbital plane and each other. This
formula approximates well more cumbersome expressions obtained from the fit
with numerical simulations. By integrating over all equally likely orientations
for precessing mergers we determine a lower approximant to the final spin
distribution as function of the mass ratio alone. By folding this with the
derived mass ratio dependent merger rate we derive a lower bound to the typical
final spin value after mergers. We repeat the procedure deriving an upper bound
for the typical spin in the case when the spins are aligned to the orbital
angular momentum, such that there is no precession in the system. Both slopes
of $\chi_{f}$ as function of the initial spins being smaller than one lead to
two attractors at $\chi_{f}^{prec}=0.2$ and $\chi_{f}^{align}=0.45$,
respectively. Real mergers, biased toward partial alignment by interactions
with the environment (accretion, host galaxy, etc.) would generate a typical
final spin lying between these two limiting values. These are the typical
values of the spin after the merger, starting from which the spin can built up
by further gaseous accretion.
A direct measurement of the baryonic mass function of galaxies & implications for the galactic baryon fraction. (arXiv:1208.5229v1 [astro-ph.CO])
A direct measurement of the baryonic mass function of galaxies & implications for the galactic baryon fraction. (arXiv:1208.5229v1 [astro-ph.CO]):
We use both an HI-selected and an optically-selected galaxy sample to
directly measure the abundance of galaxies as a function of their "baryonic"
mass (stars + atomic gas). Stellar masses are calculated based on optical data
from the Sloan Digital Sky Survey (SDSS) and atomic gas masses are calculated
using atomic hydrogen (HI) emission line data from the Arecibo Legacy Fast ALFA
(ALFALFA) survey. By using the technique of abundance matching, we combine the
measured baryonic function (BMF) of galaxies with the dark matter halo mass
function in a LCDM universe, in order to determine the galactic baryon fraction
as a function of host halo mass. We find that the baryon fraction of low-mass
halos is much smaller than the cosmic value, even when atomic gas is taken into
account. We find that the galactic baryon deficit increases monotonically with
decreasing halo mass, in contrast with previous studies which suggested an
approximately constant baryon fraction at the low-mass end. We argue that the
observed baryon fractions of low mass halos cannot be explained by reionization
heating alone, and that additional feedback mechanisms (e.g. supernova blowout)
must be invoked. However, the outflow rates needed to reproduce our result are
not easily accommodated in the standard picture of galaxy formation in a LCDM
universe.
We use both an HI-selected and an optically-selected galaxy sample to
directly measure the abundance of galaxies as a function of their "baryonic"
mass (stars + atomic gas). Stellar masses are calculated based on optical data
from the Sloan Digital Sky Survey (SDSS) and atomic gas masses are calculated
using atomic hydrogen (HI) emission line data from the Arecibo Legacy Fast ALFA
(ALFALFA) survey. By using the technique of abundance matching, we combine the
measured baryonic function (BMF) of galaxies with the dark matter halo mass
function in a LCDM universe, in order to determine the galactic baryon fraction
as a function of host halo mass. We find that the baryon fraction of low-mass
halos is much smaller than the cosmic value, even when atomic gas is taken into
account. We find that the galactic baryon deficit increases monotonically with
decreasing halo mass, in contrast with previous studies which suggested an
approximately constant baryon fraction at the low-mass end. We argue that the
observed baryon fractions of low mass halos cannot be explained by reionization
heating alone, and that additional feedback mechanisms (e.g. supernova blowout)
must be invoked. However, the outflow rates needed to reproduce our result are
not easily accommodated in the standard picture of galaxy formation in a LCDM
universe.
Magnetism in Dense Quark Matter. (arXiv:1208.5179v1 [nucl-th])
Magnetism in Dense Quark Matter. (arXiv:1208.5179v1 [nucl-th]):
We review the mechanisms via which an external magnetic field can affect the
ground state of cold and dense quark matter. In the absence of a magnetic
field, at asymptotically high densities, cold quark matter is in the
Color-Flavor-Locked (CFL) phase of color superconductivity characterized by
three scales: the superconducting gap, the gluon Meissner mass, and the
baryonic chemical potential. When an applied magnetic field becomes comparable
with each of these scales, new phases and/or condensates may emerge. They
include the magnetic CFL (MCFL) phase that becomes relevant for fields of the
order of the gap scale; the paramagnetic CFL, important when the field is of
the order of the Meissner mass, and a spin-one condensate associated to the
magnetic moment of the Cooper pairs, significant at fields of the order of the
chemical potential. We discuss the equation of state (EoS) of MCFL matter for a
large range of field values and consider possible applications of the magnetic
effects on dense quark matter to the astrophysics of compact stars.
We review the mechanisms via which an external magnetic field can affect the
ground state of cold and dense quark matter. In the absence of a magnetic
field, at asymptotically high densities, cold quark matter is in the
Color-Flavor-Locked (CFL) phase of color superconductivity characterized by
three scales: the superconducting gap, the gluon Meissner mass, and the
baryonic chemical potential. When an applied magnetic field becomes comparable
with each of these scales, new phases and/or condensates may emerge. They
include the magnetic CFL (MCFL) phase that becomes relevant for fields of the
order of the gap scale; the paramagnetic CFL, important when the field is of
the order of the Meissner mass, and a spin-one condensate associated to the
magnetic moment of the Cooper pairs, significant at fields of the order of the
chemical potential. We discuss the equation of state (EoS) of MCFL matter for a
large range of field values and consider possible applications of the magnetic
effects on dense quark matter to the astrophysics of compact stars.
Comoving Space Density and Obscured Fraction of High-Redshift Active Galactic Nuclei in the Subaru/{\it XMM-Newton} Deep Survey. (arXiv:1208.5050v1 [astro-ph.CO])
Comoving Space Density and Obscured Fraction of High-Redshift Active Galactic Nuclei in the Subaru/{\it XMM-Newton} Deep Survey. (arXiv:1208.5050v1 [astro-ph.CO]):
We study the comoving space density of X-ray-selected luminous active
galactic nuclei (AGNs) and the obscured AGN fraction at high redshifts ($3 < z
< 5$) in the Subaru/{\it XMM-Newton} Deep Survey (SXDS) field. From an X-ray
source catalog with high completeness of optical identification thanks to deep
optical images, we select a sample of 30 AGNs at $z > 3$ with intrinsic
(de-absorbed and rest-frame 2--10 keV) luminosities of $L_{\rm X} = 10^{44-45}$
erg s$^{-1}$ detected in the 0.5--2 keV band, consisting of 20 and 10 objects
with spectroscopic and photometric redshifts, respectively. Utilizing the
$1/V_{\rm max}$ method, we confirm that the comoving space density of luminous
AGNs decreases with redshift above $z > 3$. When combined with the {\it
Chandra}-COSMOS result of Civano et al.\ (2011), the density decline of AGNs
with $L_{\rm X} = 10^{44-45}$ erg s$^{-1}$ is well represented by a power law
of $(1 + z)^{-6.2 \pm 0.9}$. We also determine the fraction of X-ray obscured
AGNs with $N_{\rm H} > 10^{22}$ cm$^{-2}$ in the Compton-thin population to be
0.54$^{+0.17}_{-0.19}$, by carefully taking into account observational biases
including the effects of photon statistics for each source. This result is
consistent with an independent determination of the type-2 AGN fraction based
on optical properties, for which the fraction is found to be 0.59$\pm$0.09.
Comparing our result with that obtained in the local Universe, we conclude that
the obscured fraction of luminous AGNs increases significantly from $z=0$ to
$z>3$ by a factor of 2.5$\pm$1.1.
We study the comoving space density of X-ray-selected luminous active
galactic nuclei (AGNs) and the obscured AGN fraction at high redshifts ($3 < z
< 5$) in the Subaru/{\it XMM-Newton} Deep Survey (SXDS) field. From an X-ray
source catalog with high completeness of optical identification thanks to deep
optical images, we select a sample of 30 AGNs at $z > 3$ with intrinsic
(de-absorbed and rest-frame 2--10 keV) luminosities of $L_{\rm X} = 10^{44-45}$
erg s$^{-1}$ detected in the 0.5--2 keV band, consisting of 20 and 10 objects
with spectroscopic and photometric redshifts, respectively. Utilizing the
$1/V_{\rm max}$ method, we confirm that the comoving space density of luminous
AGNs decreases with redshift above $z > 3$. When combined with the {\it
Chandra}-COSMOS result of Civano et al.\ (2011), the density decline of AGNs
with $L_{\rm X} = 10^{44-45}$ erg s$^{-1}$ is well represented by a power law
of $(1 + z)^{-6.2 \pm 0.9}$. We also determine the fraction of X-ray obscured
AGNs with $N_{\rm H} > 10^{22}$ cm$^{-2}$ in the Compton-thin population to be
0.54$^{+0.17}_{-0.19}$, by carefully taking into account observational biases
including the effects of photon statistics for each source. This result is
consistent with an independent determination of the type-2 AGN fraction based
on optical properties, for which the fraction is found to be 0.59$\pm$0.09.
Comparing our result with that obtained in the local Universe, we conclude that
the obscured fraction of luminous AGNs increases significantly from $z=0$ to
$z>3$ by a factor of 2.5$\pm$1.1.
Monday, August 27, 2012
Background X-ray Radiation Fields Produced by Young Embedded Star Clusters
Background X-ray Radiation Fields Produced by Young Embedded Star Clusters
Most star formation in our galaxy occurs within embedded clusters, and these background environments can affect the star and planet formation processes occurring within them. In turn, young stellar members can shape the background environment and thereby provide a feedback mechanism. This work explores one aspect of stellar feedback by quantifying the background X-ray radiation fields produced by young stellar objects. Specifically, the distributions of X-ray luminosities and X-ray fluxes produced by cluster environments are constructed as a function of cluster membership size $N$. Composite flux distributions, for given distributions of cluster sizes $N$, are also constructed. The resulting distributions are wide and the X-ray radiation fields are moderately intense, with the expected flux levels exceeding the cosmic and galactic X-ray backgrounds by factors of $\sim10-1000$ (for energies 0.2 -- 15 keV). For circumstellar disks that are geometrically thin and optically thick, the X-ray flux from the background cluster dominates that provided by a typical central star in the outer disk where $r \ga 9 - 14$ AU. In addition, the expectation value of the ionization rate provided by the cluster X-ray background is $\zeta_X\sim8\times10^{-17}$ s$^{-1}$, about 4 -- 8 times larger than the canonical value of the ionization rate from cosmic rays. These elevated flux levels in clusters indicate that X-rays can affect ionization, chemistry, and heating in circumstellar disks and in the material between young stellar objects.
Most star formation in our galaxy occurs within embedded clusters, and these background environments can affect the star and planet formation processes occurring within them. In turn, young stellar members can shape the background environment and thereby provide a feedback mechanism. This work explores one aspect of stellar feedback by quantifying the background X-ray radiation fields produced by young stellar objects. Specifically, the distributions of X-ray luminosities and X-ray fluxes produced by cluster environments are constructed as a function of cluster membership size $N$. Composite flux distributions, for given distributions of cluster sizes $N$, are also constructed. The resulting distributions are wide and the X-ray radiation fields are moderately intense, with the expected flux levels exceeding the cosmic and galactic X-ray backgrounds by factors of $\sim10-1000$ (for energies 0.2 -- 15 keV). For circumstellar disks that are geometrically thin and optically thick, the X-ray flux from the background cluster dominates that provided by a typical central star in the outer disk where $r \ga 9 - 14$ AU. In addition, the expectation value of the ionization rate provided by the cluster X-ray background is $\zeta_X\sim8\times10^{-17}$ s$^{-1}$, about 4 -- 8 times larger than the canonical value of the ionization rate from cosmic rays. These elevated flux levels in clusters indicate that X-rays can affect ionization, chemistry, and heating in circumstellar disks and in the material between young stellar objects.
FUV and X-ray irradiated protoplanetary disks: a grid of models I. The disk structure. (arXiv:1208.4959v1 [astro-ph.SR])
FUV and X-ray irradiated protoplanetary disks: a grid of models I. The disk structure. (arXiv:1208.4959v1 [astro-ph.SR]):
Context. Planets are thought to eventually form from the mostly gaseous (~99%
of the mass) disks around young stars. The density structure and chemical
composition of protoplanetary disks are affected by the incident radiation
field at optical, FUV, and X-ray wavelengths, as well as by the dust
properties.
Aims. The effect of FUV and X-rays on the disk structure and the gas chemical
composition are investigated. This work forms the basis of a second paper,
which discusses the impact on diagnostic lines of, e.g., C+, O, H2O, and Ne+
observed with facilities such as Spitzer and Herschel.
Methods. A grid of 240 models is computed in which the X-ray and FUV
luminosity, minimum grain size, dust size distribution, and surface density
distribution are varied in a systematic way. The hydrostatic structure and the
thermo-chemical structure are calculated using ProDiMo.
Results. The abundance structure of neutral oxygen is stable to changes in
the X-ray and FUV luminosity, and the emission lines will thus be useful
tracers of the disk mass and temperature. The C+ abundance distribution is
sensitive to both X-rays and FUV. The radial column density profile shows two
peaks, one at the inner rim and a second one at a radius r=5-10 AU. Ne+ and
other heavy elements have a very strong response to X-rays, and the column
density in the inner disk increases by two orders of magnitude from the lowest
(LX = 1e29 erg/s) to the highest considered X-ray flux (LX = 1e32 erg/s). FUV
confines the Ne+ ionized region to areas closer to the star at low X-ray
luminosities (LX = 1e29 erg/s). H2O abundances are enhanced by X-rays due to
higher temperatures in the inner disk and higher ionization fractions in the
outer disk. The line fluxes and profiles are affected by the effects on these
species, thus providing diagnostic value in the study of FUV and X-ray
irradiated disks around T Tauri stars. (abridged)
Context. Planets are thought to eventually form from the mostly gaseous (~99%
of the mass) disks around young stars. The density structure and chemical
composition of protoplanetary disks are affected by the incident radiation
field at optical, FUV, and X-ray wavelengths, as well as by the dust
properties.
Aims. The effect of FUV and X-rays on the disk structure and the gas chemical
composition are investigated. This work forms the basis of a second paper,
which discusses the impact on diagnostic lines of, e.g., C+, O, H2O, and Ne+
observed with facilities such as Spitzer and Herschel.
Methods. A grid of 240 models is computed in which the X-ray and FUV
luminosity, minimum grain size, dust size distribution, and surface density
distribution are varied in a systematic way. The hydrostatic structure and the
thermo-chemical structure are calculated using ProDiMo.
Results. The abundance structure of neutral oxygen is stable to changes in
the X-ray and FUV luminosity, and the emission lines will thus be useful
tracers of the disk mass and temperature. The C+ abundance distribution is
sensitive to both X-rays and FUV. The radial column density profile shows two
peaks, one at the inner rim and a second one at a radius r=5-10 AU. Ne+ and
other heavy elements have a very strong response to X-rays, and the column
density in the inner disk increases by two orders of magnitude from the lowest
(LX = 1e29 erg/s) to the highest considered X-ray flux (LX = 1e32 erg/s). FUV
confines the Ne+ ionized region to areas closer to the star at low X-ray
luminosities (LX = 1e29 erg/s). H2O abundances are enhanced by X-rays due to
higher temperatures in the inner disk and higher ionization fractions in the
outer disk. The line fluxes and profiles are affected by the effects on these
species, thus providing diagnostic value in the study of FUV and X-ray
irradiated disks around T Tauri stars. (abridged)
Thursday, August 23, 2012
Black hole binary OJ287 as a testing platform for general relativity. (arXiv:1208.4524v1 [astro-ph.HE])
Black hole binary OJ287 as a testing platform for general relativity. (arXiv:1208.4524v1 [astro-ph.HE]):
The blazar OJ287 is the most promising (and the only) case for an
extragalactic binary black hole system inspiralling under the action of
gravitational radiation reaction. At present, though it is not possible to
directly observe the binary components, it is possible to observe the jet
emanating form the primary black hole. We argue that the orbital motion of the
secondary black hole is reflected in the wobble of the jet and demonstrate that
the wobble is orbital position dependent. The erratic wobble of the jet,
reported in Agudo et al. (2012), is analyzed by taking into account the binary
nature of the system and we find that the erratic component of jet wobble is
very small.
The blazar OJ287 is the most promising (and the only) case for an
extragalactic binary black hole system inspiralling under the action of
gravitational radiation reaction. At present, though it is not possible to
directly observe the binary components, it is possible to observe the jet
emanating form the primary black hole. We argue that the orbital motion of the
secondary black hole is reflected in the wobble of the jet and demonstrate that
the wobble is orbital position dependent. The erratic wobble of the jet,
reported in Agudo et al. (2012), is analyzed by taking into account the binary
nature of the system and we find that the erratic component of jet wobble is
very small.
The Disk-Wind-Jet Connection in the Black Hole H 1743-322. (arXiv:1208.4514v1 [astro-ph.HE])
The Disk-Wind-Jet Connection in the Black Hole H 1743-322. (arXiv:1208.4514v1 [astro-ph.HE]):
X-ray disk winds are detected in spectrally soft, disk-dominated phases of
stellar-mass black hole outbursts. In contrast, compact, steady, relativistic
jets are detected in spectrally hard states that are dominated by non-thermal
X-ray emission. Although these distinctive outflows appear to be almost
mutually exclusive, it is possible that a disk wind persists in hard states but
cannot be detected via X-ray absorption lines owing to very high ionization.
Here, we present an analysis of a deep, 60 ksec Chandra/HETGS observation of
the black hole candidate H 1743-322 in the low/hard state. The spectrum shows
no evidence of a disk wind, with tight limits, and within the range of ionizing
flux levels that were measured in prior Chandra observations wherein a wind was
clearly detected. In H 1743-322, at least, disk winds are actually diminished
in the low/hard state, and disk winds and jets are likely state-dependent and
anti-correlated. These results suggest that although the launching radii of
winds and jets may differ by orders of magnitude, they may both be tied to a
fundamental property of the inner accretion flow, such as the mass accretion
rate and/or the magnetic field topology of the disk. We discuss these results
in the context of disk winds and jets in other stellar-mass black holes, and
possible launching mechanisms for black hole outflows.
X-ray disk winds are detected in spectrally soft, disk-dominated phases of
stellar-mass black hole outbursts. In contrast, compact, steady, relativistic
jets are detected in spectrally hard states that are dominated by non-thermal
X-ray emission. Although these distinctive outflows appear to be almost
mutually exclusive, it is possible that a disk wind persists in hard states but
cannot be detected via X-ray absorption lines owing to very high ionization.
Here, we present an analysis of a deep, 60 ksec Chandra/HETGS observation of
the black hole candidate H 1743-322 in the low/hard state. The spectrum shows
no evidence of a disk wind, with tight limits, and within the range of ionizing
flux levels that were measured in prior Chandra observations wherein a wind was
clearly detected. In H 1743-322, at least, disk winds are actually diminished
in the low/hard state, and disk winds and jets are likely state-dependent and
anti-correlated. These results suggest that although the launching radii of
winds and jets may differ by orders of magnitude, they may both be tied to a
fundamental property of the inner accretion flow, such as the mass accretion
rate and/or the magnetic field topology of the disk. We discuss these results
in the context of disk winds and jets in other stellar-mass black holes, and
possible launching mechanisms for black hole outflows.
Tuesday, August 21, 2012
A Weak-Lensing Mass Reconstruction of the Large-Scale Filament Feeding the Massive Galaxy Cluster MACSJ0717.5+3745. (arXiv:1208.4323v1 [astro-ph.CO])
A Weak-Lensing Mass Reconstruction of the Large-Scale Filament Feeding the Massive Galaxy Cluster MACSJ0717.5+3745. (arXiv:1208.4323v1 [astro-ph.CO]):
We report the first weak-lensing detection of a large-scale filament
funneling matter onto the core of the massive galaxy cluster MACSJ0717.5+3745.
Our analysis is based on a mosaic of 18 multi-passband images obtained with ACS
aboard the HST, covering an area of \sim 10x20 arcmin^2. We use a weak-lensing
pipeline developed for the COSMOS survey, modified for the analysis of galaxy
clusters, to produce a weak-lensing catalogue. A mass map is then computed by
applying a weak-gravitational-lensing multi-scale reconstruction technique
designed to describe irregular mass distributions such as the one investigated
here. We test the resulting mass map by comparing the mass distribution
inferred for the cluster core with the one derived from strong-lensing
constraints and find excellent agreement. The filament is detected within the 3
sigma detection contour of the lensing mass reconstruction, and underlines the
importance of filaments for theoretical and numerical models of the mass
distribution in the Cosmic Web. We measure the filament's projected length as
\sim 4.5 h_{74}^{-1} Mpc, and its mean density as (2.92 \pm 0.66)10^8 h_{74}
M_{\odot} kpc^{-2}. Combined with the redshift distribution of galaxies
obtained after an extensive spectroscopic follow-up in the area, we can rule
out any projection effect resulting from the chance alignment on the sky of
unrelated galaxy group-scale structures. Assuming plausible constraints
concerning the structure's geometry based on its galaxy velocity field, we
construct a 3D model of the large-scale filament. Within this framework, we
derive the three-dimensional length of the filament to be 18 h_{74}^{-1} Mpc,
and a deprojected density in terms of the critical density of the Universe of
(206 \pm 46) \rho_{crit}, a value that lies at the very high end of the range
predicted by numerical simulations.
We report the first weak-lensing detection of a large-scale filament
funneling matter onto the core of the massive galaxy cluster MACSJ0717.5+3745.
Our analysis is based on a mosaic of 18 multi-passband images obtained with ACS
aboard the HST, covering an area of \sim 10x20 arcmin^2. We use a weak-lensing
pipeline developed for the COSMOS survey, modified for the analysis of galaxy
clusters, to produce a weak-lensing catalogue. A mass map is then computed by
applying a weak-gravitational-lensing multi-scale reconstruction technique
designed to describe irregular mass distributions such as the one investigated
here. We test the resulting mass map by comparing the mass distribution
inferred for the cluster core with the one derived from strong-lensing
constraints and find excellent agreement. The filament is detected within the 3
sigma detection contour of the lensing mass reconstruction, and underlines the
importance of filaments for theoretical and numerical models of the mass
distribution in the Cosmic Web. We measure the filament's projected length as
\sim 4.5 h_{74}^{-1} Mpc, and its mean density as (2.92 \pm 0.66)10^8 h_{74}
M_{\odot} kpc^{-2}. Combined with the redshift distribution of galaxies
obtained after an extensive spectroscopic follow-up in the area, we can rule
out any projection effect resulting from the chance alignment on the sky of
unrelated galaxy group-scale structures. Assuming plausible constraints
concerning the structure's geometry based on its galaxy velocity field, we
construct a 3D model of the large-scale filament. Within this framework, we
derive the three-dimensional length of the filament to be 18 h_{74}^{-1} Mpc,
and a deprojected density in terms of the critical density of the Universe of
(206 \pm 46) \rho_{crit}, a value that lies at the very high end of the range
predicted by numerical simulations.
The nature of the unresolved extragalactic soft CXB. (arXiv:1208.4105v1 [astro-ph.CO])
The nature of the unresolved extragalactic soft CXB. (arXiv:1208.4105v1 [astro-ph.CO]):
In this paper we investigate the power spectrum of the unresolved 0.5-2 keV
CXB with deep Chandra 4 Ms observations in the CDFS. We measured a signal
which, on scales >30", is significantly higher than the Shot-Noise and is
increasing with the angular scale. We interpreted this signal as the joint
contribution of clustered undetected sources like AGN, Galaxies and
Inter-Galactic-Medium (IGM). The power of unresolved cosmic sources
fluctuations accounts for \sim 12% of the 0.5-2 keV extragalactic CXB. Overall,
our modeling predicts that \sim 20% of the unresolved CXB flux is made by low
luminosity AGN, \sim 25% by galaxies and \sim 55% by the IGM (Inter Galactic
Medium). We do not find any direct evidence of the so called Warm Hot
Intergalactic Medium (i.e. matter with 10^5K<T<10^7K and density contrast
{\delta} <1000), but we estimated that it could produce about 1/7 of the
unresolved CXB. We placed an upper limit to the space density of postulated
X-ray-emitting early black hole at z>7.5 and compared it with SMBH evolution
models.
In this paper we investigate the power spectrum of the unresolved 0.5-2 keV
CXB with deep Chandra 4 Ms observations in the CDFS. We measured a signal
which, on scales >30", is significantly higher than the Shot-Noise and is
increasing with the angular scale. We interpreted this signal as the joint
contribution of clustered undetected sources like AGN, Galaxies and
Inter-Galactic-Medium (IGM). The power of unresolved cosmic sources
fluctuations accounts for \sim 12% of the 0.5-2 keV extragalactic CXB. Overall,
our modeling predicts that \sim 20% of the unresolved CXB flux is made by low
luminosity AGN, \sim 25% by galaxies and \sim 55% by the IGM (Inter Galactic
Medium). We do not find any direct evidence of the so called Warm Hot
Intergalactic Medium (i.e. matter with 10^5K<T<10^7K and density contrast
{\delta} <1000), but we estimated that it could produce about 1/7 of the
unresolved CXB. We placed an upper limit to the space density of postulated
X-ray-emitting early black hole at z>7.5 and compared it with SMBH evolution
models.
Nucleosynthetic Layers in the Shocked Ejecta of Cassiopeia A. (arXiv:1208.4034v1 [astro-ph.SR])
Nucleosynthetic Layers in the Shocked Ejecta of Cassiopeia A. (arXiv:1208.4034v1 [astro-ph.SR]):
We present a 3-dimensional analysis of the supernova remnant Cassiopeia A
using high resolution spectra from the Spitzer Space Telescope. We observe
supernova ejecta both immediately before and during the shock-ejecta
interaction. We determine that the reverse shock of the remnant is spherical to
within 7%, although the center of this sphere is offset from the geometric
center of the remnant by 810 km/s. We determine that the velocity width of the
nucleosynthetic layers is approximately 1000 km/s over 4000 square arcsecond
regions, although the velocity width of a layer along any individual line of
sight is <250 km/s. Si and O, which come from different nucleosynthetic layers
in the progenitor star, are observed to be coincident in velocity space in some
directions, but segregated by up to approximately 500 km/s in other directions.
We compare these observations of the nucleosynthetic layers to predictions from
supernova explosion models in an attempt to constrain such models. Finally, we
observe small-scale, corrugated velocity structures that are likely caused
during the supernova explosion itself, rather than hundreds of years later by
dynamical instabilities at the remnant's reverse shock.
We present a 3-dimensional analysis of the supernova remnant Cassiopeia A
using high resolution spectra from the Spitzer Space Telescope. We observe
supernova ejecta both immediately before and during the shock-ejecta
interaction. We determine that the reverse shock of the remnant is spherical to
within 7%, although the center of this sphere is offset from the geometric
center of the remnant by 810 km/s. We determine that the velocity width of the
nucleosynthetic layers is approximately 1000 km/s over 4000 square arcsecond
regions, although the velocity width of a layer along any individual line of
sight is <250 km/s. Si and O, which come from different nucleosynthetic layers
in the progenitor star, are observed to be coincident in velocity space in some
directions, but segregated by up to approximately 500 km/s in other directions.
We compare these observations of the nucleosynthetic layers to predictions from
supernova explosion models in an attempt to constrain such models. Finally, we
observe small-scale, corrugated velocity structures that are likely caused
during the supernova explosion itself, rather than hundreds of years later by
dynamical instabilities at the remnant's reverse shock.
The dark matter distribution in z~0.5 clusters of galaxies. I : Determining scaling relations with weak lensing masses. (arXiv:1208.4026v1 [astro-ph.CO])
The dark matter distribution in z~0.5 clusters of galaxies. I : Determining scaling relations with weak lensing masses. (arXiv:1208.4026v1 [astro-ph.CO]):
The total mass of clusters of galaxies is a key parameter to study massive
halos. It relates to numerous gravitational and baryonic processes at play in
the framework of large scale structure formation, thus rendering its
determination important but challenging. From a sample of the 11 X-ray bright
clusters selected from the excpres sample, we investigate the optical and X-ray
properties of clusters with respect to their total mass derived from weak
gravitational lensing. From multi-color wide field imaging obtained with
MegaCam at CFHT, we derive the shear profile of each individual cluster of
galaxies. We perform a careful investigation of all systematic sources related
to the weak lensing mass determination. The weak lensing masses are then
compared to the X-ray masses obtained from the analysis of XMM observations and
assuming hydrostatic equilibrium. We find a good agreement between the two mass
proxies although a few outliers with either perturbed morphology or poor
quality data prevent to derive robust mass estimates. The weak lensing mass is
also correlated with the optical richness and the total optical luminosity, as
well as with the X-ray luminosity, to provide scaling relations within the
redshift range 0.4<z<0.6. These relations are in good agreement with previous
works at lower redshifts. For the L_X-M relation we combine our sample with two
other cluster and group samples from the literature, thus covering two decades
in mass and X-ray luminosity, with a regular and coherent correlation between
the two physical quantities.
The total mass of clusters of galaxies is a key parameter to study massive
halos. It relates to numerous gravitational and baryonic processes at play in
the framework of large scale structure formation, thus rendering its
determination important but challenging. From a sample of the 11 X-ray bright
clusters selected from the excpres sample, we investigate the optical and X-ray
properties of clusters with respect to their total mass derived from weak
gravitational lensing. From multi-color wide field imaging obtained with
MegaCam at CFHT, we derive the shear profile of each individual cluster of
galaxies. We perform a careful investigation of all systematic sources related
to the weak lensing mass determination. The weak lensing masses are then
compared to the X-ray masses obtained from the analysis of XMM observations and
assuming hydrostatic equilibrium. We find a good agreement between the two mass
proxies although a few outliers with either perturbed morphology or poor
quality data prevent to derive robust mass estimates. The weak lensing mass is
also correlated with the optical richness and the total optical luminosity, as
well as with the X-ray luminosity, to provide scaling relations within the
redshift range 0.4<z<0.6. These relations are in good agreement with previous
works at lower redshifts. For the L_X-M relation we combine our sample with two
other cluster and group samples from the literature, thus covering two decades
in mass and X-ray luminosity, with a regular and coherent correlation between
the two physical quantities.
Too massive neutron stars: The role of dark matter?. (arXiv:1208.3722v1 [astro-ph.SR])
Too massive neutron stars: The role of dark matter?. (arXiv:1208.3722v1 [astro-ph.SR]):
The maximum mass of a neutron star is generally determined by the equation of
state of the star material. In this study, we take into account dark matter
particles, assumed to behave like fermions with a free parameter to account for
the interaction strength among the particles, as a possible constituent of
neutron stars. We find dark matter inside the star would soften the equation of
state more strongly than that of hyperons, and reduce largely the maximum mass
of the star. However, the neutron star maximum mass is sensitive to the
particle mass of dark matter, and a very high neutron star mass larger than 2
times solar mass could be achieved when the particle mass is small enough. Such
kind of dark-matter- admixed neutron stars could explain the recent measurement
of the Shapiro delay in the radio pulsar PSR J1614-2230, which yielded a
neutron star mass of 2 times solar mass that may be hardly reached when
hyperons are considered only, as in the case of the microscopic Brueckner
theory. Furthermore, in this particular case, we point out that the dark matter
around a neutron star should also contribute to the mass measurement due to its
pure gravitational effect. However, our numerically calculation illustrates
that such contribution could be safely ignored because of the usual diluted
dark matter environment assumed. We conclude that a very high mass measurement
of about 2 times solar mass requires a really stiff equation of state in
neutron stars, and find a strong upper limit (<= 0.64 GeV) for the particle
mass of non-self- annihilating dark matter based on the present model.
The maximum mass of a neutron star is generally determined by the equation of
state of the star material. In this study, we take into account dark matter
particles, assumed to behave like fermions with a free parameter to account for
the interaction strength among the particles, as a possible constituent of
neutron stars. We find dark matter inside the star would soften the equation of
state more strongly than that of hyperons, and reduce largely the maximum mass
of the star. However, the neutron star maximum mass is sensitive to the
particle mass of dark matter, and a very high neutron star mass larger than 2
times solar mass could be achieved when the particle mass is small enough. Such
kind of dark-matter- admixed neutron stars could explain the recent measurement
of the Shapiro delay in the radio pulsar PSR J1614-2230, which yielded a
neutron star mass of 2 times solar mass that may be hardly reached when
hyperons are considered only, as in the case of the microscopic Brueckner
theory. Furthermore, in this particular case, we point out that the dark matter
around a neutron star should also contribute to the mass measurement due to its
pure gravitational effect. However, our numerically calculation illustrates
that such contribution could be safely ignored because of the usual diluted
dark matter environment assumed. We conclude that a very high mass measurement
of about 2 times solar mass requires a really stiff equation of state in
neutron stars, and find a strong upper limit (<= 0.64 GeV) for the particle
mass of non-self- annihilating dark matter based on the present model.
Monday, August 20, 2012
Planck Intermediate Results. X. Physics of the hot gas in the Coma cluster. (arXiv:1208.3611v1 [astro-ph.CO])
Planck Intermediate Results. X. Physics of the hot gas in the Coma cluster. (arXiv:1208.3611v1 [astro-ph.CO]):
We present an analysis of Planck satellite data on the Coma Cluster observed
via the Sunyaev-Zeldovich effect. Planck is able, for the first time, to detect
SZ emission up to r ~ 3 X R_500. We test previously proposed models for the
pressure distribution in clusters against the azimuthally averaged data. We
find that the Arnaud et al. universal pressure profile does not fit Coma, and
that their pressure profile for merging systems provides a good fit of the data
only at r<R_500: by r=2XR_500 it underestimates the observed y profile by a
factor of ~2. This may indicate that at these larger radii either i) the
cluster SZ emission is contaminated by unresolved SZ sources along the line of
sight or ii) the pressure profile of Coma is higher at r>R_500 than the mean
pressure profile predicted by the simulations. The Planck image shows
significant local steepening of the y profile in two regions about half a
degree to the west and to the south-east of the cluster centre. These features
are consistent with the presence of shock fronts at these radii, and indeed the
western feature was previously noticed in the ROSAT PSPC mosaic by Markevitch
(2000) as well as in the radio. Using Planck y profiles extracted from
corresponding sectors we find pressure jumps of 4.5+2.5-0.1 and 4.9+0.7-0.2 in
the west and southeast, respectively. Assuming Rankine-Hugoniot pressure jump
conditions, we deduce that the shock waves should propagate with Mach number
M_w=1.95+0.45-0.02 and M_se=2.03+0.14-0.04 in the West and Southeast,
respectively. Finally, we find that the y and radio-synchrotron signals are
quasi-linearly correlated on Mpc scales with small intrinsic scatter. This
implies either that the energy density of cosmic-ray electrons is relatively
constant throughout the cluster, or that the magnetic fields fall off much more
slowly with radius than previously thought.
We present an analysis of Planck satellite data on the Coma Cluster observed
via the Sunyaev-Zeldovich effect. Planck is able, for the first time, to detect
SZ emission up to r ~ 3 X R_500. We test previously proposed models for the
pressure distribution in clusters against the azimuthally averaged data. We
find that the Arnaud et al. universal pressure profile does not fit Coma, and
that their pressure profile for merging systems provides a good fit of the data
only at r<R_500: by r=2XR_500 it underestimates the observed y profile by a
factor of ~2. This may indicate that at these larger radii either i) the
cluster SZ emission is contaminated by unresolved SZ sources along the line of
sight or ii) the pressure profile of Coma is higher at r>R_500 than the mean
pressure profile predicted by the simulations. The Planck image shows
significant local steepening of the y profile in two regions about half a
degree to the west and to the south-east of the cluster centre. These features
are consistent with the presence of shock fronts at these radii, and indeed the
western feature was previously noticed in the ROSAT PSPC mosaic by Markevitch
(2000) as well as in the radio. Using Planck y profiles extracted from
corresponding sectors we find pressure jumps of 4.5+2.5-0.1 and 4.9+0.7-0.2 in
the west and southeast, respectively. Assuming Rankine-Hugoniot pressure jump
conditions, we deduce that the shock waves should propagate with Mach number
M_w=1.95+0.45-0.02 and M_se=2.03+0.14-0.04 in the West and Southeast,
respectively. Finally, we find that the y and radio-synchrotron signals are
quasi-linearly correlated on Mpc scales with small intrinsic scatter. This
implies either that the energy density of cosmic-ray electrons is relatively
constant throughout the cluster, or that the magnetic fields fall off much more
slowly with radius than previously thought.
Friday, August 17, 2012
The Formation and Evolution of Massive Black Holes
The Formation and Evolution of Massive Black Holes
The past 10 years have witnessed a change of perspective in the way astrophysicists think about massive black holes (MBHs), which are now considered to have a major role in the evolution of galaxies. This appreciation was driven by the realization that black holes of millions solar masses and above reside in the center of most galaxies, including the Milky Way. MBHs also powered active galactic nuclei known to exist just a few hundred million years after the Big Bang. Here, I summarize the current ideas on the evolution of MBHs through cosmic history, from their formation about 13 billion years ago to their growth within their host galaxies
Benchmarking atomic data for astrophysics: a first look at the soft X-ray lines. (arXiv:1208.2142v1 [astro-ph.SR])
Benchmarking atomic data for astrophysics: a first look at the soft X-ray lines. (arXiv:1208.2142v1 [astro-ph.SR]):
A collection of the best solar and laboratory spectra in the soft X-rays is
used here to perform a preliminary benchmark in this wavelength region, by
comparing observed vs. predicted wavelengths and calibrated solar irradiances.
The benchmark focuses on the Fe IX - Fe XIV ions,for which we have recently
calculated the relevant atomic data, however a few other ions have also been
benchmarked. The iron ions are dominating the soft X-rays, however a large
fraction of the strongest soft X-ray lines due to n=4 -> n=3 transitions were
previously unidentified. The strongest transitions are all identified here, in
particular the decays from the core-excited levels (3s 3p^l 4s, l=$ 5,4,3,2,1
for Fe X, Fe XI, Fe XII, Fe XIII, and Fe XIV respectively) which are the
strongest soft X-ray transitions from these ions. Many new identifications are
proposed, some only tentatively. Good agreement in terms of solar irradiances
between the soft X-ray and EUV (n=3 -> n=3) transitions is found, confirming
the reliability of the new large-scale calculations. Some of the new atomic
data and identifications are particularly important for the Solar Dynamic
Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94 A band.
A collection of the best solar and laboratory spectra in the soft X-rays is
used here to perform a preliminary benchmark in this wavelength region, by
comparing observed vs. predicted wavelengths and calibrated solar irradiances.
The benchmark focuses on the Fe IX - Fe XIV ions,for which we have recently
calculated the relevant atomic data, however a few other ions have also been
benchmarked. The iron ions are dominating the soft X-rays, however a large
fraction of the strongest soft X-ray lines due to n=4 -> n=3 transitions were
previously unidentified. The strongest transitions are all identified here, in
particular the decays from the core-excited levels (3s 3p^l 4s, l=$ 5,4,3,2,1
for Fe X, Fe XI, Fe XII, Fe XIII, and Fe XIV respectively) which are the
strongest soft X-ray transitions from these ions. Many new identifications are
proposed, some only tentatively. Good agreement in terms of solar irradiances
between the soft X-ray and EUV (n=3 -> n=3) transitions is found, confirming
the reliability of the new large-scale calculations. Some of the new atomic
data and identifications are particularly important for the Solar Dynamic
Observatory (SDO) Atmospheric Imaging Assembly (AIA) 94 A band.
Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae. (arXiv:1208.2094v1 [astro-ph.HE])
Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae. (arXiv:1208.2094v1 [astro-ph.HE]):
We perform multi-dimensional, time-dependent radiation transfer simulations
for hard X-ray and $\gamma$-ray emissions, following radioactive decays of
$^{56}$Ni and $^{56}$Co, for two-dimensional delayed detonation models of Type
Ia supernovae (SNe Ia). The synthetic spectra and light curves are compared
with the sensitivities of current and future observatories with an exposure of
$10^6$ seconds. The non-detection of the $\gamma$-ray signal from SN 2011fe at
6.4 Mpc by SPI on board INTEGRAL places the upper limit for the mass of
$^{56}$Ni as $\lsim$1.0 M_{\odot}$ independently from observations in any
other wavelengths. Signals from the newly formed radioactive species have not
been convincingly measured yet from any SN Ia, but the future X-ray and
$\gamma$-ray missions are expected to deepen the observable horizon to provide
the high energy emission data for a significant SN Ia sample. We predict that
the hard X-ray detectors on board NuStar or ASTRO-H, launched in 2012 and to be
so in 2014, will reach to SNe Ia at $\sim$15 Mpc, i.e., one SN in a few years.
Furthermore, according to the present results, the soft $\gamma$-ray detector
on board ASTRO-H will be able to detect the 158 keV line emission up to
$\sim$25 Mpc, i.e., a few SNe Ia per year. Proposed next generation
$\gamma$-ray missions, e.g., GRIPS, could reach to SNe Ia at $\sim$20 - 35$
Mpc by MeV observations. Those would provide new diagnostics and strong
constraints on explosion models, detecting rather directly the main energy
source of supernova light.
We perform multi-dimensional, time-dependent radiation transfer simulations
for hard X-ray and $\gamma$-ray emissions, following radioactive decays of
$^{56}$Ni and $^{56}$Co, for two-dimensional delayed detonation models of Type
Ia supernovae (SNe Ia). The synthetic spectra and light curves are compared
with the sensitivities of current and future observatories with an exposure of
$10^6$ seconds. The non-detection of the $\gamma$-ray signal from SN 2011fe at
6.4 Mpc by SPI on board INTEGRAL places the upper limit for the mass of
$^{56}$Ni as $\lsim$1.0 M_{\odot}$ independently from observations in any
other wavelengths. Signals from the newly formed radioactive species have not
been convincingly measured yet from any SN Ia, but the future X-ray and
$\gamma$-ray missions are expected to deepen the observable horizon to provide
the high energy emission data for a significant SN Ia sample. We predict that
the hard X-ray detectors on board NuStar or ASTRO-H, launched in 2012 and to be
so in 2014, will reach to SNe Ia at $\sim$15 Mpc, i.e., one SN in a few years.
Furthermore, according to the present results, the soft $\gamma$-ray detector
on board ASTRO-H will be able to detect the 158 keV line emission up to
$\sim$25 Mpc, i.e., a few SNe Ia per year. Proposed next generation
$\gamma$-ray missions, e.g., GRIPS, could reach to SNe Ia at $\sim$20 - 35$
Mpc by MeV observations. Those would provide new diagnostics and strong
constraints on explosion models, detecting rather directly the main energy
source of supernova light.
The Dark Matter Haloes of Chandra X-ray Galaxy Clusters and Baryons Effect. (arXiv:1208.2424v1 [astro-ph.CO])
The Dark Matter Haloes of Chandra X-ray Galaxy Clusters and Baryons Effect. (arXiv:1208.2424v1 [astro-ph.CO]):
We present results based on Chandra observations of a large sample of 129 hot
galaxy clusters. We measure the concentration parameter c_200, the dark mass
M_200 and the baryonic mass content in all the objects of our sample, providing
the largest dataset of mass parameters for galaxy clusters in the redshift
range z = 0.01 -- 1.4. We confirm that a tight correlation between c_200 and
M_200, c \propto M^a_{vir}/(1+z)^b with a = -0.56 +/- 0.15 and b = 0.80 +/-
0.25 (68 per cent confidence limits), is present, in good agreement with the
predictions from numerical simulations and previous observations.
The inner slope $\alpha$ of the total mass density profile (\rho(r)\propto
r^{-\alpha}) is derived from the slope of the integrated mass profile, using a
generalized NFW model. The values of the inner slope \alpha, is \alpha = 0.94
+/- 0.13.
Finally, we show that the inner slope of the density profile, \alpha
correlates with the baryonic mass content, M_b: namely \alpha is decreasing
with increasing baryonic mass content.
We present results based on Chandra observations of a large sample of 129 hot
galaxy clusters. We measure the concentration parameter c_200, the dark mass
M_200 and the baryonic mass content in all the objects of our sample, providing
the largest dataset of mass parameters for galaxy clusters in the redshift
range z = 0.01 -- 1.4. We confirm that a tight correlation between c_200 and
M_200, c \propto M^a_{vir}/(1+z)^b with a = -0.56 +/- 0.15 and b = 0.80 +/-
0.25 (68 per cent confidence limits), is present, in good agreement with the
predictions from numerical simulations and previous observations.
The inner slope $\alpha$ of the total mass density profile (\rho(r)\propto
r^{-\alpha}) is derived from the slope of the integrated mass profile, using a
generalized NFW model. The values of the inner slope \alpha, is \alpha = 0.94
+/- 0.13.
Finally, we show that the inner slope of the density profile, \alpha
correlates with the baryonic mass content, M_b: namely \alpha is decreasing
with increasing baryonic mass content.
Large-scale Motions in the Perseus Galaxy Cluster. (arXiv:1208.2990v1 [astro-ph.CO])
Large-scale Motions in the Perseus Galaxy Cluster. (arXiv:1208.2990v1 [astro-ph.CO]):
By combining large-scale mosaics of ROSAT PSPC, XMM-Newton, and Suzaku X-ray
observations, we present evidence for large-scale motions in the intracluster
medium of the nearby, X-ray bright Perseus Cluster. These motions are suggested
by several alternating and interleaved X-ray bright, low-temperature,
low-entropy arcs located along the east-west axis, at radii ranging from ~10
kpc to over a Mpc. Thermodynamic features qualitatively similar to these have
previously been observed in the centers of cool core clusters, and were
successfully modeled as a consequence of the gas sloshing/swirling motions
induced by minor mergers. Our observations indicate that such sloshing/swirling
can extend out to larger radii than previously thought, on scales approaching
the virial radius.
By combining large-scale mosaics of ROSAT PSPC, XMM-Newton, and Suzaku X-ray
observations, we present evidence for large-scale motions in the intracluster
medium of the nearby, X-ray bright Perseus Cluster. These motions are suggested
by several alternating and interleaved X-ray bright, low-temperature,
low-entropy arcs located along the east-west axis, at radii ranging from ~10
kpc to over a Mpc. Thermodynamic features qualitatively similar to these have
previously been observed in the centers of cool core clusters, and were
successfully modeled as a consequence of the gas sloshing/swirling motions
induced by minor mergers. Our observations indicate that such sloshing/swirling
can extend out to larger radii than previously thought, on scales approaching
the virial radius.
A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster. (arXiv:1208.2962v1 [astro-ph.CO])
A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster. (arXiv:1208.2962v1 [astro-ph.CO]):
In the cores of some galaxy clusters the hot intracluster plasma is dense
enough that it should cool radiatively in the cluster's lifetime, leading to
continuous "cooling flows" of gas sinking towards the cluster center, yet no
such cooling flow has been observed. The low observed star formation rates and
cool gas masses for these "cool core" clusters suggest that much of the cooling
must be offset by astrophysical feedback to prevent the formation of a runaway
cooling flow. Here we report X-ray, optical, and infrared observations of the
galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an
exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which
hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further,
the central galaxy in this cluster appears to be experiencing a massive
starburst (740 +/- 160 Msun/yr), which suggests that the feedback source
responsible for preventing runaway cooling in nearby cool core clusters may not
yet be fully established in SPT-CLJ2344-4243. This large star formation rate
implies that a significant fraction of the stars in the central galaxy of this
cluster may form via accretion of the intracluster medium, rather than the
current picture of central galaxies assembling entirely via mergers.
In the cores of some galaxy clusters the hot intracluster plasma is dense
enough that it should cool radiatively in the cluster's lifetime, leading to
continuous "cooling flows" of gas sinking towards the cluster center, yet no
such cooling flow has been observed. The low observed star formation rates and
cool gas masses for these "cool core" clusters suggest that much of the cooling
must be offset by astrophysical feedback to prevent the formation of a runaway
cooling flow. Here we report X-ray, optical, and infrared observations of the
galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an
exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which
hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further,
the central galaxy in this cluster appears to be experiencing a massive
starburst (740 +/- 160 Msun/yr), which suggests that the feedback source
responsible for preventing runaway cooling in nearby cool core clusters may not
yet be fully established in SPT-CLJ2344-4243. This large star formation rate
implies that a significant fraction of the stars in the central galaxy of this
cluster may form via accretion of the intracluster medium, rather than the
current picture of central galaxies assembling entirely via mergers.
Pygmies, Giants, and Skins. (arXiv:1208.3417v1 [nucl-th])
Pygmies, Giants, and Skins. (arXiv:1208.3417v1 [nucl-th]):
Understanding the equation of state (EOS) of neutron-rich matter is a central
goal of nuclear physics that cuts across a variety of disciplines. Indeed, the
limits of nuclear existence, the collision of energetic heavy ions, the
structure of neutron stars, and the dynamics of core-collapse supernova all
depend critically on the nuclear-matter EOS. In this contribution I focus on
the EOS of cold baryonic matter with special emphasis on its impact on the
structure, dynamics, and composition of neutron stars. In particular, I discuss
how laboratory experiments on neutron skins as well as on Pygmy and Giant
resonances can help us elucidate the structure of these fascinating objects.
Understanding the equation of state (EOS) of neutron-rich matter is a central
goal of nuclear physics that cuts across a variety of disciplines. Indeed, the
limits of nuclear existence, the collision of energetic heavy ions, the
structure of neutron stars, and the dynamics of core-collapse supernova all
depend critically on the nuclear-matter EOS. In this contribution I focus on
the EOS of cold baryonic matter with special emphasis on its impact on the
structure, dynamics, and composition of neutron stars. In particular, I discuss
how laboratory experiments on neutron skins as well as on Pygmy and Giant
resonances can help us elucidate the structure of these fascinating objects.
High-Redshift Cool-Core Galaxy Clusters Detected via the Sunyaev-Zel'dovich Effect in the South Pole Telescope Survey. (arXiv:1208.3368v1 [astro-ph.CO])
High-Redshift Cool-Core Galaxy Clusters Detected via the Sunyaev-Zel'dovich Effect in the South Pole Telescope Survey. (arXiv:1208.3368v1 [astro-ph.CO]):
We report the first investigation of cool-core properties of galaxy clusters
selected via their Sunyaev-Zel'dovich (SZ) effect. We use 13 galaxy clusters
uniformly selected from 178 deg^2 observed with the South Pole Telescope (SPT)
and followed-up by the Chandra X-ray Observatory. They form an approximately
mass-limited sample (> 3 x 10^14 M_sun h^-1_70) spanning redshifts 0.3 < z <
1.1. Using previously published X-ray--selected cluster samples, we compare two
proxies of cool-core strength: surface brightness concentration (cSB) and
cuspiness ({\alpha}). We find cSB is better constrained. We measure cSB for the
SPT sample and find several new z > 0.5 cool-core clusters, including two
strong cool cores. This rules out the hypothesis that there are no z > 0.5
clusters that qualify as strong cool cores at the 5.4{\sigma} level. The
fraction of strong cool-core clusters in the SPT sample in this redshift regime
is between 7% and 56% (95% confidence). Although the SPT selection function is
significantly different from the X-ray samples, the high-z cSB distribution for
the SPT sample is statistically consistent with that of X-ray--selected samples
at both low and high redshifts. The cool-core strength is inversely correlated
with the offset between the brightest cluster galaxy and the X-ray centroid,
providing evidence that the dynamical state affects the cool-core strength of
the cluster. Larger SZ-selected samples will be crucial in understanding the
evolution of cluster cool cores over cosmic time.
We report the first investigation of cool-core properties of galaxy clusters
selected via their Sunyaev-Zel'dovich (SZ) effect. We use 13 galaxy clusters
uniformly selected from 178 deg^2 observed with the South Pole Telescope (SPT)
and followed-up by the Chandra X-ray Observatory. They form an approximately
mass-limited sample (> 3 x 10^14 M_sun h^-1_70) spanning redshifts 0.3 < z <
1.1. Using previously published X-ray--selected cluster samples, we compare two
proxies of cool-core strength: surface brightness concentration (cSB) and
cuspiness ({\alpha}). We find cSB is better constrained. We measure cSB for the
SPT sample and find several new z > 0.5 cool-core clusters, including two
strong cool cores. This rules out the hypothesis that there are no z > 0.5
clusters that qualify as strong cool cores at the 5.4{\sigma} level. The
fraction of strong cool-core clusters in the SPT sample in this redshift regime
is between 7% and 56% (95% confidence). Although the SPT selection function is
significantly different from the X-ray samples, the high-z cSB distribution for
the SPT sample is statistically consistent with that of X-ray--selected samples
at both low and high redshifts. The cool-core strength is inversely correlated
with the offset between the brightest cluster galaxy and the X-ray centroid,
providing evidence that the dynamical state affects the cool-core strength of
the cluster. Larger SZ-selected samples will be crucial in understanding the
evolution of cluster cool cores over cosmic time.
Multiple views of magnetism in cool stars. (arXiv:1208.3338v1 [astro-ph.SR])
Multiple views of magnetism in cool stars. (arXiv:1208.3338v1 [astro-ph.SR]):
Magnetic fields are regarded as a crucial element for our understanding of
stellar physics. They can be studied with a variety of methods which provide
complementary - and sometimes contradictory - information about the structure,
strength and dynamics of the magnetic field and its role in the evolution of
stars. Stellar magnetic fields can be investigated either with direct methods
based on the Zeeman effect or through the observation of activity phenomena
resulting from the interaction of the field with the stellar atmosphere. In
this Cool Stars XVII Splinter Session we discussed the results obtained by the
many ongoing studies of stellar activity and direct studies of surface magnetic
fields, as well as the state- of-the-art techniques on which they are based. We
show the strengths and limitations of the various approaches currently used and
to point out their evolution as well as the interest of coupling various
magnetism and activity proxies.
Magnetic fields are regarded as a crucial element for our understanding of
stellar physics. They can be studied with a variety of methods which provide
complementary - and sometimes contradictory - information about the structure,
strength and dynamics of the magnetic field and its role in the evolution of
stars. Stellar magnetic fields can be investigated either with direct methods
based on the Zeeman effect or through the observation of activity phenomena
resulting from the interaction of the field with the stellar atmosphere. In
this Cool Stars XVII Splinter Session we discussed the results obtained by the
many ongoing studies of stellar activity and direct studies of surface magnetic
fields, as well as the state- of-the-art techniques on which they are based. We
show the strengths and limitations of the various approaches currently used and
to point out their evolution as well as the interest of coupling various
magnetism and activity proxies.
X-ray polarimetry as a new tool to discriminate reflection from absorption scenarios -- Predictions for MCG-6-30-15. (arXiv:1208.3314v1 [astro-ph.HE])
X-ray polarimetry as a new tool to discriminate reflection from absorption scenarios -- Predictions for MCG-6-30-15. (arXiv:1208.3314v1 [astro-ph.HE]):
We present modelling of X-ray polarisation spectra emerging from the two
competing scenarios that are proposed to explain the broad Fe K{\alpha} line in
the Seyfert 1 galaxy MCG-6-30-15. The polarisation signature of complex
absorption is studied for a partial covering scenario using a clumpy wind and
compared to a reflection model based on the lamp-post geometry. The shape of
the polarisation percentage and angle as a function of photon energy are found
to be distinctly different between the reflection and the absorption case.
Relativistic reflection produces significantly stronger polarisation in the
1-10 keV energy band than absorption. The spectrum of the polarisation angle
adds additional constraints: in the absorption case it shows a constant shape,
whereas the relativistic reflection scenario typically leads to a smooth
rotation of the polarisation angle with photon energy. Based on this work, we
conclude that a soft X-ray polarimeter on-board a small X-ray satellite may
already discriminate between the absorption and the reflection scenario. A
promising opportunity may arise with the X-ray Imaging Polarimetry Explorer
(XIPE) mission, which has been proposed to ESA in response to a small-size
(S-class) mission call due for launch in 2017.
We present modelling of X-ray polarisation spectra emerging from the two
competing scenarios that are proposed to explain the broad Fe K{\alpha} line in
the Seyfert 1 galaxy MCG-6-30-15. The polarisation signature of complex
absorption is studied for a partial covering scenario using a clumpy wind and
compared to a reflection model based on the lamp-post geometry. The shape of
the polarisation percentage and angle as a function of photon energy are found
to be distinctly different between the reflection and the absorption case.
Relativistic reflection produces significantly stronger polarisation in the
1-10 keV energy band than absorption. The spectrum of the polarisation angle
adds additional constraints: in the absorption case it shows a constant shape,
whereas the relativistic reflection scenario typically leads to a smooth
rotation of the polarisation angle with photon energy. Based on this work, we
conclude that a soft X-ray polarimeter on-board a small X-ray satellite may
already discriminate between the absorption and the reflection scenario. A
promising opportunity may arise with the X-ray Imaging Polarimetry Explorer
(XIPE) mission, which has been proposed to ESA in response to a small-size
(S-class) mission call due for launch in 2017.
Evidence of Light-Bending Effects and its implication for spectral state transitions. (arXiv:1208.3277v1 [astro-ph.HE])
Evidence of Light-Bending Effects and its implication for spectral state transitions. (arXiv:1208.3277v1 [astro-ph.HE]):
It has long been speculated that the nature of the hard X-ray corona may be
an important second driver of black hole state transitions, in addition to the
mass accretion rate through the disk. However, a clear physical picture of
coronal changes has not yet emerged. We present results from a systematic
analysis of Rossi X-ray Timing Explorer observations of the stellar mass black
hole binary XTE J1650-500. All spectra with significant hard X-ray detections
were fit using a self-consistent, relativistically-blurred disk reflection
model suited to high ionization regimes. Importantly, we find evidence that
both the spectral and timing properties of black hole states may be partially
driven by the height of the X-ray corona above the disk, and related changes in
how gravitational light bending affects the corona--disk interaction.
Specifically, the evolution of the power-law, thermal disk, and
relativistically--convolved reflection components in our spectral analysis
indicate that: (1) the disk inner radius remains constant at $r_{in}
=1.65\pm0.08 GM/c^2$ (consistent with values found for the ISCO of XTE
J1650-500 in other works) throughout the transition from the brighter phases of
the low-hard state to the intermediate states (both the hard-intermediate and
soft-intermediate), through to the soft state and back; (2) the ratio between
the observed reflected X-ray flux and power-law continuum (the "reflection
fraction", $R$) increases sharply at the transition between the
hard-intermediate and soft-intermediate states ("cannonball" jets are sometimes
launched at this transition); (3) both the frequency and coherence of the
high-frequency quasi-periodic oscillations (QPOs) observed in XTE J1650-500
increase with $R$. We discuss our results in terms of black hole states and the
nature of black hole accretion flows across the mass scale.
It has long been speculated that the nature of the hard X-ray corona may be
an important second driver of black hole state transitions, in addition to the
mass accretion rate through the disk. However, a clear physical picture of
coronal changes has not yet emerged. We present results from a systematic
analysis of Rossi X-ray Timing Explorer observations of the stellar mass black
hole binary XTE J1650-500. All spectra with significant hard X-ray detections
were fit using a self-consistent, relativistically-blurred disk reflection
model suited to high ionization regimes. Importantly, we find evidence that
both the spectral and timing properties of black hole states may be partially
driven by the height of the X-ray corona above the disk, and related changes in
how gravitational light bending affects the corona--disk interaction.
Specifically, the evolution of the power-law, thermal disk, and
relativistically--convolved reflection components in our spectral analysis
indicate that: (1) the disk inner radius remains constant at $r_{in}
=1.65\pm0.08 GM/c^2$ (consistent with values found for the ISCO of XTE
J1650-500 in other works) throughout the transition from the brighter phases of
the low-hard state to the intermediate states (both the hard-intermediate and
soft-intermediate), through to the soft state and back; (2) the ratio between
the observed reflected X-ray flux and power-law continuum (the "reflection
fraction", $R$) increases sharply at the transition between the
hard-intermediate and soft-intermediate states ("cannonball" jets are sometimes
launched at this transition); (3) both the frequency and coherence of the
high-frequency quasi-periodic oscillations (QPOs) observed in XTE J1650-500
increase with $R$. We discuss our results in terms of black hole states and the
nature of black hole accretion flows across the mass scale.
Identifying the Baryons in a Multiphase Intergalactic Medium. (arXiv:1208.3249v1 [astro-ph.CO])
Identifying the Baryons in a Multiphase Intergalactic Medium. (arXiv:1208.3249v1 [astro-ph.CO]):
In this white paper, we summarize current observations of the baryon census
at low redshift (Shull, Smith, & Danforth 2012). Measurements of Lya, O-VI, and
broad Lya absorbers, together with more careful corrections for metallicity and
ionization fraction, can now account for approximately 60% of the baryons in
the intergalactic medium (IGM). An additional 5 +/- 3% may reside in the
circumgalactic medium (CGM), 7 +/- 2% in galaxies, and 4 +/- 1.5% in clusters.
This still leaves a substantial fraction, 29 +/- 13%, unaccounted for. We
suggest improvements in measuring the baryons in major components of the IGM
and CGM with future Ultraviolet and X-ray spectrographs. These missions could
find and map the missing baryons, the fuel for the formation and chemical
evolution of galaxies.
In this white paper, we summarize current observations of the baryon census
at low redshift (Shull, Smith, & Danforth 2012). Measurements of Lya, O-VI, and
broad Lya absorbers, together with more careful corrections for metallicity and
ionization fraction, can now account for approximately 60% of the baryons in
the intergalactic medium (IGM). An additional 5 +/- 3% may reside in the
circumgalactic medium (CGM), 7 +/- 2% in galaxies, and 4 +/- 1.5% in clusters.
This still leaves a substantial fraction, 29 +/- 13%, unaccounted for. We
suggest improvements in measuring the baryons in major components of the IGM
and CGM with future Ultraviolet and X-ray spectrographs. These missions could
find and map the missing baryons, the fuel for the formation and chemical
evolution of galaxies.
Sunday, August 12, 2012
The equation of state of neutron star matter and the symmetry energy. (arXiv:1208.1736v1 [nucl-th])
The equation of state of neutron star matter and the symmetry energy. (arXiv:1208.1736v1 [nucl-th]):
We present an overview of microscopical calculations of the Equation of State
(EOS) of neutron matter performed using Quantum Monte Carlo techniques. We
focus to the role of the model of the three-neutron force in the high-density
part of the EOS up to a few times the saturation density. We also discuss the
interplay between the symmetry energy and the neutron star mass-radius
relation.
The combination of theoretical models of the EOS with recent neutron stars
observations permits us to constrain the value of the symmetry energy and its
slope. We show that astrophysical observations are starting to provide
important insights into the properties of neutron star matter.
We present an overview of microscopical calculations of the Equation of State
(EOS) of neutron matter performed using Quantum Monte Carlo techniques. We
focus to the role of the model of the three-neutron force in the high-density
part of the EOS up to a few times the saturation density. We also discuss the
interplay between the symmetry energy and the neutron star mass-radius
relation.
The combination of theoretical models of the EOS with recent neutron stars
observations permits us to constrain the value of the symmetry energy and its
slope. We show that astrophysical observations are starting to provide
important insights into the properties of neutron star matter.
Exploring X-ray and radio emission of type 1 AGN up to z ~ 2.3. (arXiv:1208.1716v1 [astro-ph.CO])
Exploring X-ray and radio emission of type 1 AGN up to z ~ 2.3. (arXiv:1208.1716v1 [astro-ph.CO]):
X-ray emission from AGN is dominated by the accretion disk around a SMBH. The
radio luminosity, however, has not such a clear origin except in the most
powerful sources where jets are evident. The origin (and even the very
existence) of the local bi-modal distribution in radioloudness is also a
debated issue. By analysing X-ray, optical and radio properties of a large
sample of type 1 AGN up to z>2, where the bulk of this population resides, we
aim to explore the interplay between radio and X-ray emission in AGN, in order
to further our knowledge on the origin of radio emission, and its relation to
accretion. We analyse a large (~800 sources) sample of type 1 AGN and QSOs
selected from the 2XMMi X-ray source catalogue, cross-correlated with the SDSS
DR7 spectroscopic catalogue, covering a redshift range from z~0.3 to z~2.3.
SMBH masses are estimated from the Mg II emission line, bolometric luminosities
from the X-ray data, and radio emission or upper limits from the FIRST
catalogue. Most of the sources accrete close to the Eddington limit and the
distribution in radioloudness does not appear to have a bi-modal behaviour. We
confirm that radioloud AGN are also X-ray loud, with an X-ray-to-optical ratio
up to twice that of radioquiet objects, even excluding the most extreme
strongly jetted sources. By analysing complementary radio-selected control
samples, we find evidence that these conclusions are not an effect of the X-ray
selection, but are likely a property of the dominant QSO population. Our
findings are best interpreted in a context where radio emission in AGN, with
the exception of a minority of beamed sources, arises from very close to the
accretion disk and is therefore heavily linked to X-ray emission. We also
speculate that the RL/RQ dichotomy might either be an evolutionary effect that
developed well after the QSO peak epoch, or an effect of incompleteness in
small samples.
X-ray emission from AGN is dominated by the accretion disk around a SMBH. The
radio luminosity, however, has not such a clear origin except in the most
powerful sources where jets are evident. The origin (and even the very
existence) of the local bi-modal distribution in radioloudness is also a
debated issue. By analysing X-ray, optical and radio properties of a large
sample of type 1 AGN up to z>2, where the bulk of this population resides, we
aim to explore the interplay between radio and X-ray emission in AGN, in order
to further our knowledge on the origin of radio emission, and its relation to
accretion. We analyse a large (~800 sources) sample of type 1 AGN and QSOs
selected from the 2XMMi X-ray source catalogue, cross-correlated with the SDSS
DR7 spectroscopic catalogue, covering a redshift range from z~0.3 to z~2.3.
SMBH masses are estimated from the Mg II emission line, bolometric luminosities
from the X-ray data, and radio emission or upper limits from the FIRST
catalogue. Most of the sources accrete close to the Eddington limit and the
distribution in radioloudness does not appear to have a bi-modal behaviour. We
confirm that radioloud AGN are also X-ray loud, with an X-ray-to-optical ratio
up to twice that of radioquiet objects, even excluding the most extreme
strongly jetted sources. By analysing complementary radio-selected control
samples, we find evidence that these conclusions are not an effect of the X-ray
selection, but are likely a property of the dominant QSO population. Our
findings are best interpreted in a context where radio emission in AGN, with
the exception of a minority of beamed sources, arises from very close to the
accretion disk and is therefore heavily linked to X-ray emission. We also
speculate that the RL/RQ dichotomy might either be an evolutionary effect that
developed well after the QSO peak epoch, or an effect of incompleteness in
small samples.
X-ray photoionized bubble in the wind of Vela X-1 pulsar supergiant companion. (arXiv:1208.1827v1 [astro-ph.SR])
X-ray photoionized bubble in the wind of Vela X-1 pulsar supergiant companion. (arXiv:1208.1827v1 [astro-ph.SR]):
Vela X-1 is the archetype of high-mass X-ray binaries, composed of a neutron
star and a massive B supergiant. The supergiant is a source of a strong
radiatively-driven stellar wind. The neutron star sweeps up this wind, and
creates a huge amount of X-rays as a result of energy release during the
process of wind accretion. Here we provide detailed NLTE models of the Vela X-1
envelope. We study how the X-rays photoionize the wind and destroy the ions
responsible for the wind acceleration. The resulting decrease of the radiative
force explains the observed reduction of the wind terminal velocity in a
direction to the neutron star. The X-rays create a distinct photoionized region
around the neutron star filled with a stagnating flow. The existence of such
photoionized bubbles is a general property of high-mass X-ray binaries. We
unveiled a new principle governing these complex objects, according to which
there is an upper limit to the X-ray luminosity the compact star can have
without suspending the wind due to inefficient line driving
Vela X-1 is the archetype of high-mass X-ray binaries, composed of a neutron
star and a massive B supergiant. The supergiant is a source of a strong
radiatively-driven stellar wind. The neutron star sweeps up this wind, and
creates a huge amount of X-rays as a result of energy release during the
process of wind accretion. Here we provide detailed NLTE models of the Vela X-1
envelope. We study how the X-rays photoionize the wind and destroy the ions
responsible for the wind acceleration. The resulting decrease of the radiative
force explains the observed reduction of the wind terminal velocity in a
direction to the neutron star. The X-rays create a distinct photoionized region
around the neutron star filled with a stagnating flow. The existence of such
photoionized bubbles is a general property of high-mass X-ray binaries. We
unveiled a new principle governing these complex objects, according to which
there is an upper limit to the X-ray luminosity the compact star can have
without suspending the wind due to inefficient line driving
Miscentring in Galaxy Clusters: Dark Matter to Brightest Cluster Galaxy Offsets in 10,000 SDSS Clusters. (arXiv:1208.1766v1 [astro-ph.CO])
Miscentring in Galaxy Clusters: Dark Matter to Brightest Cluster Galaxy Offsets in 10,000 SDSS Clusters. (arXiv:1208.1766v1 [astro-ph.CO]):
We characterise the typical offset between the Dark Matter (DM) projected
centre and the Brightest Cluster Galaxy (BCG) in 10,000 SDSS clusters. To place
constraints on the centre of DM, we use an automated strong-lensing analysis,
mass-modelling technique which is based on the well-tested assumption that
light traces mass. The cluster galaxies are modelled with a steep power-law,
and the DM component is obtained by smoothing the galaxy distribution fitting a
low-order 2D polynomial (via spline interpolation), while probing a whole range
of polynomial degrees and galaxy power laws. We find that the offsets between
the BCG and the peak of the smoothed light map representing the DM, \Delta, are
distributed equally around zero with no preferred direction, and are well
described by a log-normal distribution with <log_{10}(\Delta [h^{-1}
Mpc])>=-1.895^{+0.003}_{-0.004}, and \sigma=0.501\pm0.004 (95% confidence
levels), or <log_{10}(\Delta [\arcsec])>=0.564\pm0.005, and
\sigma=0.475\pm0.007. Some of the offsets originate in prior misidentifications
of the BCG or other bright cluster members by the cluster finding algorithm,
whose level we make an additional effort to assess, finding that ~10% of the
clusters in the probed catalogue are likely to be misidentified, contributing
to higher-end offsets in general agreement with previous studies. Our results
constitute the first statistically-significant high-resolution distributions of
DM-to-BCG offsets obtained in an observational analysis, and importantly show
that there exists such a typical non-zero offset in the probed catalogue. The
offsets show a weak positive correlation with redshift, so that higher
separations are generally found for higher-z clusters in agreement with the
hierarchical growth of structure, which in turn could help characterise the
merger, relaxation and evolution history of clusters, in future studies.
[ABRIDGED]
RKS Note: Could this be even better done with eROSITA data?
We characterise the typical offset between the Dark Matter (DM) projected
centre and the Brightest Cluster Galaxy (BCG) in 10,000 SDSS clusters. To place
constraints on the centre of DM, we use an automated strong-lensing analysis,
mass-modelling technique which is based on the well-tested assumption that
light traces mass. The cluster galaxies are modelled with a steep power-law,
and the DM component is obtained by smoothing the galaxy distribution fitting a
low-order 2D polynomial (via spline interpolation), while probing a whole range
of polynomial degrees and galaxy power laws. We find that the offsets between
the BCG and the peak of the smoothed light map representing the DM, \Delta, are
distributed equally around zero with no preferred direction, and are well
described by a log-normal distribution with <log_{10}(\Delta [h^{-1}
Mpc])>=-1.895^{+0.003}_{-0.004}, and \sigma=0.501\pm0.004 (95% confidence
levels), or <log_{10}(\Delta [\arcsec])>=0.564\pm0.005, and
\sigma=0.475\pm0.007. Some of the offsets originate in prior misidentifications
of the BCG or other bright cluster members by the cluster finding algorithm,
whose level we make an additional effort to assess, finding that ~10% of the
clusters in the probed catalogue are likely to be misidentified, contributing
to higher-end offsets in general agreement with previous studies. Our results
constitute the first statistically-significant high-resolution distributions of
DM-to-BCG offsets obtained in an observational analysis, and importantly show
that there exists such a typical non-zero offset in the probed catalogue. The
offsets show a weak positive correlation with redshift, so that higher
separations are generally found for higher-z clusters in agreement with the
hierarchical growth of structure, which in turn could help characterise the
merger, relaxation and evolution history of clusters, in future studies.
[ABRIDGED]
RKS Note: Could this be even better done with eROSITA data?
Wednesday, August 8, 2012
On the Weak-Wind Problem in Massive Stars: X-ray Spectra Reveal a Massive Hot Wind in \mu\ Columbae. (arXiv:1208.0820v1 [astro-ph.SR])
On the Weak-Wind Problem in Massive Stars: X-ray Spectra Reveal a Massive Hot Wind in \mu\ Columbae. (arXiv:1208.0820v1 [astro-ph.SR]):
\mu\ Columbae is a prototypical weak-wind O-star for which we have obtained a
high-resolution X-ray spectrum with the Chandra LETG/ACIS-S instrument and a
low resolution spectrum with Suzaku. This allows us, for the first time, to
investigate the role of X-rays on the wind structure in a bona fide weak-wind
system and to determine whether there actually is a massive, hot wind. The
X-ray emission measure indicates that the outflow is an order of magnitude
greater than that derived from UV lines and is commensurate with the nominal
wind-luminosity relationship for O-stars. Therefore, the ``weak-wind
problem''---identified from cool wind UV/optical spectra---is largely resolved
by accounting for the hot wind seen in X-rays. From X-ray line profiles,
Doppler shifts, and relative strengths, we find that this weak-wind star is
typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically
confined plasma---the spectrum is soft and lines are broadened; Suzaku spectra
confirm the lack of emission above 2 keV. Nor do the relative line shifts and
widths suggest any wind decoupling by ions. The He-like triplets indicate that
the bulk of the X-ray emission is formed rather close to the star, within 5
stellar radii. Our results challenge the idea that some OB stars are
``weak-wind'' stars that deviate from the standard wind-luminosity
relationship. The wind is not weak, but it is hot and its bulk is only
detectable in X-rays.
\mu\ Columbae is a prototypical weak-wind O-star for which we have obtained a
high-resolution X-ray spectrum with the Chandra LETG/ACIS-S instrument and a
low resolution spectrum with Suzaku. This allows us, for the first time, to
investigate the role of X-rays on the wind structure in a bona fide weak-wind
system and to determine whether there actually is a massive, hot wind. The
X-ray emission measure indicates that the outflow is an order of magnitude
greater than that derived from UV lines and is commensurate with the nominal
wind-luminosity relationship for O-stars. Therefore, the ``weak-wind
problem''---identified from cool wind UV/optical spectra---is largely resolved
by accounting for the hot wind seen in X-rays. From X-ray line profiles,
Doppler shifts, and relative strengths, we find that this weak-wind star is
typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically
confined plasma---the spectrum is soft and lines are broadened; Suzaku spectra
confirm the lack of emission above 2 keV. Nor do the relative line shifts and
widths suggest any wind decoupling by ions. The He-like triplets indicate that
the bulk of the X-ray emission is formed rather close to the star, within 5
stellar radii. Our results challenge the idea that some OB stars are
``weak-wind'' stars that deviate from the standard wind-luminosity
relationship. The wind is not weak, but it is hot and its bulk is only
detectable in X-rays.
The effect of frame dragging on the iron K alpha line in X-ray binaries. (arXiv:1208.0728v1 [astro-ph.HE])
The effect of frame dragging on the iron K alpha line in X-ray binaries. (arXiv:1208.0728v1 [astro-ph.HE]):
The clear characteristic timescale picked out by the low frequency
quasi-periodic oscillations (QPOs) seen in many black hole and neutron star
binaries has the potential to provide a very powerful diagnostic of the inner
regions of the accretion flow. However, this potential cannot be realised
without a quantitative model for the QPO. We have recently shown that the same
truncated disc/hot inner flow geometry which is used to interpret the spectral
transitions can also directly produce the QPO from Lense-Thirring (vertical)
precession of the hot inner flow. This correctly predicts both the frequency
and spectrum of the QPO, and the tight correlation of these properties with the
total spectrum of the source via a changing truncation radius between the disc
and hot flow. This model predicts a unique iron line signature as a vertically
tilted flow illuminates different azimuths of the disc as it precesses. The
iron line arising from this rotating illumination is blue shifted when the flow
irradiates the approaching region of the spinning disc and red shifted when the
flow irradiates the receding region of the disc. This gives rise to a
characteristic rocking of the iron line on the QPO frequency which is a
necessary (and probably sufficient) test of a Lense-Thirring origin. This is
also an independent test of disc truncation models for the low/hard state, as
vertical precession cannot occur if there is a disc in the midplane.
We show that it may be possible to observe this effect using archival data
from the Rossi X-ray timing explorer (RXTE) or XMM Newton. However, a clean
test requires a combination of moderate resolution and good statistics, such as
would be available from a long XMM-Newton observation or with data from the
proposed ESA mission LOFT.
The clear characteristic timescale picked out by the low frequency
quasi-periodic oscillations (QPOs) seen in many black hole and neutron star
binaries has the potential to provide a very powerful diagnostic of the inner
regions of the accretion flow. However, this potential cannot be realised
without a quantitative model for the QPO. We have recently shown that the same
truncated disc/hot inner flow geometry which is used to interpret the spectral
transitions can also directly produce the QPO from Lense-Thirring (vertical)
precession of the hot inner flow. This correctly predicts both the frequency
and spectrum of the QPO, and the tight correlation of these properties with the
total spectrum of the source via a changing truncation radius between the disc
and hot flow. This model predicts a unique iron line signature as a vertically
tilted flow illuminates different azimuths of the disc as it precesses. The
iron line arising from this rotating illumination is blue shifted when the flow
irradiates the approaching region of the spinning disc and red shifted when the
flow irradiates the receding region of the disc. This gives rise to a
characteristic rocking of the iron line on the QPO frequency which is a
necessary (and probably sufficient) test of a Lense-Thirring origin. This is
also an independent test of disc truncation models for the low/hard state, as
vertical precession cannot occur if there is a disc in the midplane.
We show that it may be possible to observe this effect using archival data
from the Rossi X-ray timing explorer (RXTE) or XMM Newton. However, a clean
test requires a combination of moderate resolution and good statistics, such as
would be available from a long XMM-Newton observation or with data from the
proposed ESA mission LOFT.
The Canadian Cluster Comparison Project: weak lensing masses and SZ scaling relations. (arXiv:1208.0606v1 [astro-ph.CO])
The Canadian Cluster Comparison Project: weak lensing masses and SZ scaling relations. (arXiv:1208.0606v1 [astro-ph.CO]):
The Canadian Cluster Comparison Project is a comprehensive multi-wavelength
survey targeting 50 massive X-ray selected clusters of galaxies to examine
baryonic tracers of cluster mass and to probe the cluster-to-cluster variation
in the thermal properties of the hot intracluster medium. In this paper we
present the weak lensing masses, based on the analysis of deep wide-field
imaging data obtained using the Canada-France-Hawaii-Telescope. The final
sample includes two additional clusters that were located in the field-of-view.
We take these masses as our reference for the comparison of cluster properties
at other wavelengths. In this paper we limit the comparison to published
measurements of the Sunyaev-Zel'dovich effect. We find that this signal
correlates well with the projected lensing mass, with an intrinsic scatter of
12\pm5% at ~r_2500, demonstrating it is an excellent proxy for cluster mass.
The Canadian Cluster Comparison Project is a comprehensive multi-wavelength
survey targeting 50 massive X-ray selected clusters of galaxies to examine
baryonic tracers of cluster mass and to probe the cluster-to-cluster variation
in the thermal properties of the hot intracluster medium. In this paper we
present the weak lensing masses, based on the analysis of deep wide-field
imaging data obtained using the Canada-France-Hawaii-Telescope. The final
sample includes two additional clusters that were located in the field-of-view.
We take these masses as our reference for the comparison of cluster properties
at other wavelengths. In this paper we limit the comparison to published
measurements of the Sunyaev-Zel'dovich effect. We find that this signal
correlates well with the projected lensing mass, with an intrinsic scatter of
12\pm5% at ~r_2500, demonstrating it is an excellent proxy for cluster mass.
Weighing the Giants III: Methods and Measurements of Accurate Galaxy Cluster Weak-Lensing Masses. (arXiv:1208.0605v1 [astro-ph.CO])
Weighing the Giants III: Methods and Measurements of Accurate Galaxy Cluster Weak-Lensing Masses. (arXiv:1208.0605v1 [astro-ph.CO]):
We report weak-lensing masses for 51 of the most X-ray luminous galaxy
clusters known. This cluster sample, introduced earlier in this series of
papers, spans redshifts 0.15 < z_cl < 0.7, and is well suited to calibrate mass
proxies for current cluster cosmology experiments. Cluster masses are measured
with a standard `color-cut' lensing method from three-filter photometry of each
field. Additionally, for 27 cluster fields with at least five-filter
photometry, we measure high-accuracy masses using a new method that exploits
all information available in the photometric redshift posterior probability
distributions of individual galaxies. Using simulations based on the COSMOS-30
catalog, we demonstrate control of systematic biases in the mean mass of the
sample with this method, from photometric redshift biases and associated
uncertainties, to better than 3%. In contrast, we show that the use of
single-point estimators in place of the full photometric redshift posterior
distributions can lead to significant redshift-dependent biases on cluster
masses. The performance of our new photometric redshift-based method allows us
to calibrate `color-cut` masses for all 51 clusters in the present sample to a
total systematic uncertainty of ~7% on the mean mass, a level sufficient to
significantly improve current cosmology constraints from galaxy clusters. Our
results bode well for future cosmological studies of clusters, potentially
reducing the need for exhaustive spectroscopic calibration surveys as compared
to other techniques, when deep, multi-filter optical and near-IR imaging
surveys are coupled with robust photometric redshift methods.
We report weak-lensing masses for 51 of the most X-ray luminous galaxy
clusters known. This cluster sample, introduced earlier in this series of
papers, spans redshifts 0.15 < z_cl < 0.7, and is well suited to calibrate mass
proxies for current cluster cosmology experiments. Cluster masses are measured
with a standard `color-cut' lensing method from three-filter photometry of each
field. Additionally, for 27 cluster fields with at least five-filter
photometry, we measure high-accuracy masses using a new method that exploits
all information available in the photometric redshift posterior probability
distributions of individual galaxies. Using simulations based on the COSMOS-30
catalog, we demonstrate control of systematic biases in the mean mass of the
sample with this method, from photometric redshift biases and associated
uncertainties, to better than 3%. In contrast, we show that the use of
single-point estimators in place of the full photometric redshift posterior
distributions can lead to significant redshift-dependent biases on cluster
masses. The performance of our new photometric redshift-based method allows us
to calibrate `color-cut` masses for all 51 clusters in the present sample to a
total systematic uncertainty of ~7% on the mean mass, a level sufficient to
significantly improve current cosmology constraints from galaxy clusters. Our
results bode well for future cosmological studies of clusters, potentially
reducing the need for exhaustive spectroscopic calibration surveys as compared
to other techniques, when deep, multi-filter optical and near-IR imaging
surveys are coupled with robust photometric redshift methods.
Weighing the Giants I: Weak Lensing Masses for 51 Massive Galaxy Clusters - Project Overview, Data Analysis Methods, and Cluster Images. (arXiv:1208.0597v1 [astro-ph.CO])
Weighing the Giants I: Weak Lensing Masses for 51 Massive Galaxy Clusters - Project Overview, Data Analysis Methods, and Cluster Images. (arXiv:1208.0597v1 [astro-ph.CO]):
This is the first in a series of papers in which we measure accurate
weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at
redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for
cosmological cluster experiments. The primary aim is to improve the absolute
mass calibration of cluster observables, currently the dominant systematic
uncertainty for cluster count experiments. Key elements of this work are the
rigorous quantification of systematic uncertainties, high-quality data
reduction and photometric calibration, and the "blind" nature of the analysis
to avoid confirmation bias. Our target clusters are drawn from RASS X-ray
catalogs, and provide a versatile calibration sample for many aspects of
cluster cosmology. We have acquired wide-field, high-quality imaging using the
Subaru and CFHT telescopes for all 51 clusters, in at least three bands per
cluster. For a subset of 27 clusters, we have data in at least five bands,
allowing accurate photo-z estimates of lensed galaxies. In this paper, we
describe the cluster sample and observations, and detail the processing of the
SuprimeCam data to yield high-quality images suitable for robust weak-lensing
shape measurements and precision photometry. For each cluster, we present
wide-field color optical images and maps of the weak-lensing mass distribution,
the optical light distribution, and the X-ray emission, providing insights into
the large-scale structure in which the clusters are embedded. We measure the
offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters,
finding these to be small in general, with a median of 20kpc. For offsets
<100kpc, weak-lensing mass measurements centered on the BCGs agree well with
values determined relative to the X-ray centroids; miscentering is therefore
not a significant source of systematic uncertainty for our mass measurements.
[abridged]
This is the first in a series of papers in which we measure accurate
weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at
redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for
cosmological cluster experiments. The primary aim is to improve the absolute
mass calibration of cluster observables, currently the dominant systematic
uncertainty for cluster count experiments. Key elements of this work are the
rigorous quantification of systematic uncertainties, high-quality data
reduction and photometric calibration, and the "blind" nature of the analysis
to avoid confirmation bias. Our target clusters are drawn from RASS X-ray
catalogs, and provide a versatile calibration sample for many aspects of
cluster cosmology. We have acquired wide-field, high-quality imaging using the
Subaru and CFHT telescopes for all 51 clusters, in at least three bands per
cluster. For a subset of 27 clusters, we have data in at least five bands,
allowing accurate photo-z estimates of lensed galaxies. In this paper, we
describe the cluster sample and observations, and detail the processing of the
SuprimeCam data to yield high-quality images suitable for robust weak-lensing
shape measurements and precision photometry. For each cluster, we present
wide-field color optical images and maps of the weak-lensing mass distribution,
the optical light distribution, and the X-ray emission, providing insights into
the large-scale structure in which the clusters are embedded. We measure the
offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters,
finding these to be small in general, with a median of 20kpc. For offsets
<100kpc, weak-lensing mass measurements centered on the BCGs agree well with
values determined relative to the X-ray centroids; miscentering is therefore
not a significant source of systematic uncertainty for our mass measurements.
[abridged]
A Suzaku survey of Fe K lines in Seyfert 1 AGN. (arXiv:1208.1150v1 [astro-ph.HE])
A Suzaku survey of Fe K lines in Seyfert 1 AGN. (arXiv:1208.1150v1 [astro-ph.HE]):
We construct full broadband models in an analysis of Suzaku observations of
nearby Seyfert 1 AGN (z<0.2) with exposures >50ks and with greater than 30000
counts in order to study their iron line profiles. This results in a sample of
46 objects and 84 observations. After a full modelling of the broadband Suzaku
and Swift-BAT data (0.6-100 keV) we find complex warm absorption is present in
59% of the objects in this sample which has a significant bearing upon the
derived Fe K region parameters. Meanwhile 35% of the 46 objects require some
degree of high column density partial coverer in order to fully model the hard
X-ray spectrum. We also find that a large number of the objects in the sample
(22%) require high velocity, high ionization outflows in the Fe K region
resulting from Fe XXV and Fe XXVI. A further four AGN feature highly ionized Fe
K absorbers consistent with zero outflow velocity, making a total of 14/46
(30%) AGN in this sample showing evidence for statistically significant
absorption in the Fe K region.
Narrow Fe K alpha emission from distant material at 6.4 keV is found to be
almost ubiquitous in these AGN. Examining the 6-7 keV Fe K region we note that
narrow emission lines originating from Fe XXV at 6.63-6.70 keV and from Fe XXVI
at 6.97 keV are present in 52% and 39% of objects respectively.
Our results suggest statistically significant relativistic Fe K alpha
emission is detected in 23 of 46 objects (50%) at >99.5% confidence, measuring
an average emissivity index of q=2.4\pm0.1 and equivalent width EW=96\pm10 eV
using the relline model. When parameterised with a Gaussian we find an average
line energy of 6.32\pm0.04 keV, sigma width=0.470\pm0.05 keV and EW=97\pm19 eV.
Where we can place constraints upon the black hole spin parameter a, we do not
require a maximally spinning black hole in all cases.
We construct full broadband models in an analysis of Suzaku observations of
nearby Seyfert 1 AGN (z<0.2) with exposures >50ks and with greater than 30000
counts in order to study their iron line profiles. This results in a sample of
46 objects and 84 observations. After a full modelling of the broadband Suzaku
and Swift-BAT data (0.6-100 keV) we find complex warm absorption is present in
59% of the objects in this sample which has a significant bearing upon the
derived Fe K region parameters. Meanwhile 35% of the 46 objects require some
degree of high column density partial coverer in order to fully model the hard
X-ray spectrum. We also find that a large number of the objects in the sample
(22%) require high velocity, high ionization outflows in the Fe K region
resulting from Fe XXV and Fe XXVI. A further four AGN feature highly ionized Fe
K absorbers consistent with zero outflow velocity, making a total of 14/46
(30%) AGN in this sample showing evidence for statistically significant
absorption in the Fe K region.
Narrow Fe K alpha emission from distant material at 6.4 keV is found to be
almost ubiquitous in these AGN. Examining the 6-7 keV Fe K region we note that
narrow emission lines originating from Fe XXV at 6.63-6.70 keV and from Fe XXVI
at 6.97 keV are present in 52% and 39% of objects respectively.
Our results suggest statistically significant relativistic Fe K alpha
emission is detected in 23 of 46 objects (50%) at >99.5% confidence, measuring
an average emissivity index of q=2.4\pm0.1 and equivalent width EW=96\pm10 eV
using the relline model. When parameterised with a Gaussian we find an average
line energy of 6.32\pm0.04 keV, sigma width=0.470\pm0.05 keV and EW=97\pm19 eV.
Where we can place constraints upon the black hole spin parameter a, we do not
require a maximally spinning black hole in all cases.
Stellar Mass Black Holes and Ultraluminous X-Ray Sources. (arXiv:1208.1138v1 [astro-ph.HE])
Stellar Mass Black Holes and Ultraluminous X-Ray Sources. (arXiv:1208.1138v1 [astro-ph.HE]):
We review the likely population, observational properties, and broad
implications of stellar-mass black holes and ultraluminous x-ray sources. We
focus on the clear empirical rules connecting accretion and outflow that have
been established for stellar-mass black holes in binary systems in the past
decade and a half. These patterns of behavior are probably the keys that will
allow us to understand black hole feedback on the largest scales over
cosmological time scales.
We review the likely population, observational properties, and broad
implications of stellar-mass black holes and ultraluminous x-ray sources. We
focus on the clear empirical rules connecting accretion and outflow that have
been established for stellar-mass black holes in binary systems in the past
decade and a half. These patterns of behavior are probably the keys that will
allow us to understand black hole feedback on the largest scales over
cosmological time scales.
A 200-s Quasi-Periodicity Following the Tidal Disruption of a Star by a Dormant Black Hole. (arXiv:1208.1046v1 [astro-ph.CO])
A 200-s Quasi-Periodicity Following the Tidal Disruption of a Star by a Dormant Black Hole. (arXiv:1208.1046v1 [astro-ph.CO]):
Supermassive black holes (SMBHs; $M\gtrsim10^5\msun$) are known to exist at
the centre of most galaxies with sufficient stellar mass. In the local
Universe, it is possible to infer their properties from the surrounding stars
or gas. However, at high redshifts we require active, continuous accretion to
infer the presence of the SMBHs, often coming in the form of long-term
accretion in active galactic nuclei. SMBHs can also capture and tidally disrupt
stars orbiting nearby, resulting in bright flares from otherwise quiescent
black holes. Here, we report on a $\sim200$-s X-ray quasi-periodicity around a
previously dormant SMBH located in the centre of a galaxy at redshift
$z=0.3534$. This result may open the possibility of probing general relativity
beyond our local Universe.
Supermassive black holes (SMBHs; $M\gtrsim10^5\msun$) are known to exist at
the centre of most galaxies with sufficient stellar mass. In the local
Universe, it is possible to infer their properties from the surrounding stars
or gas. However, at high redshifts we require active, continuous accretion to
infer the presence of the SMBHs, often coming in the form of long-term
accretion in active galactic nuclei. SMBHs can also capture and tidally disrupt
stars orbiting nearby, resulting in bright flares from otherwise quiescent
black holes. Here, we report on a $\sim200$-s X-ray quasi-periodicity around a
previously dormant SMBH located in the centre of a galaxy at redshift
$z=0.3534$. This result may open the possibility of probing general relativity
beyond our local Universe.
Self-shielding of Soft X-rays in SN Ia Progenitors. (arXiv:1208.0858v1 [astro-ph.HE])
Self-shielding of Soft X-rays in SN Ia Progenitors. (arXiv:1208.0858v1 [astro-ph.HE]):
There are insufficient super soft (~ 0.1 keV) X-ray sources in either spiral
or elliptical galaxies to account for the rate of explosion of Type Ia
supernovae in either the single degenerate or the double degenerate scenarios.
We quantify the amount of circumstellar matter that would be required to
suppress the soft X-ray flux by yielding a column density in excess of 10^{23}
cm^{-2}. We summarize evidence that appropriate quantities of matter are extant
in SN Ia and in recurrent novae that may be supernova precursors. The obscuring
matter is likely to have a large, but not complete, covering factor and to be
substantially non-spherically symmetric. Assuming that much of the absorbed
X-ray flux is re-radiated as black-body radiation in the UV, we estimate that
fewer than 100 sources might be detectable in the GALEX all sky survey.
There are insufficient super soft (~ 0.1 keV) X-ray sources in either spiral
or elliptical galaxies to account for the rate of explosion of Type Ia
supernovae in either the single degenerate or the double degenerate scenarios.
We quantify the amount of circumstellar matter that would be required to
suppress the soft X-ray flux by yielding a column density in excess of 10^{23}
cm^{-2}. We summarize evidence that appropriate quantities of matter are extant
in SN Ia and in recurrent novae that may be supernova precursors. The obscuring
matter is likely to have a large, but not complete, covering factor and to be
substantially non-spherically symmetric. Assuming that much of the absorbed
X-ray flux is re-radiated as black-body radiation in the UV, we estimate that
fewer than 100 sources might be detectable in the GALEX all sky survey.
Analytical Modeling of Galaxies at z>~6: Star Formation and Black Hole Growth. (arXiv:1208.0835v1 [astro-ph.CO])
Analytical Modeling of Galaxies at z>~6: Star Formation and Black Hole Growth. (arXiv:1208.0835v1 [astro-ph.CO]):
Galaxies at z>~6 represent an important evolutionary link between the first
galaxies and their modern counterparts. Modeling both the global and internal
properties of these recently discovered objects can lead us to understand how
they relate to even earlier systems. I show how the balance of cold inflows and
momentum-driven super-winds can explain the evolution of the UV mass-to-light
ratio from z~6--10. I then describe a model for maintaining hydrostatic
equilibrium and marginal Toomre-instability by radiation pressure in dust-free
galactic disks. Applying this framework to z~6--8 systems, I show how the
internal ISM physics can be constrained by X-rays observations with Chandra.
Galaxies at z>~6 represent an important evolutionary link between the first
galaxies and their modern counterparts. Modeling both the global and internal
properties of these recently discovered objects can lead us to understand how
they relate to even earlier systems. I show how the balance of cold inflows and
momentum-driven super-winds can explain the evolution of the UV mass-to-light
ratio from z~6--10. I then describe a model for maintaining hydrostatic
equilibrium and marginal Toomre-instability by radiation pressure in dust-free
galactic disks. Applying this framework to z~6--8 systems, I show how the
internal ISM physics can be constrained by X-rays observations with Chandra.
X-ray bursting neutron star atmosphere models using an exact relativistic kinetic equation for Compton scattering. (arXiv:1208.1467v1 [astro-ph.HE])
X-ray bursting neutron star atmosphere models using an exact relativistic kinetic equation for Compton scattering. (arXiv:1208.1467v1 [astro-ph.HE]):
Theoretical spectra of X-ray bursting neutron star (NS) model atmospheres are
widely used to determine the basic NS parameters such as their masses and
radii. We construct accurate NS atmosphere models using for the first time an
exact treatment of Compton scattering via the integral relativistic kinetic
equation. We also compare the results with the previous calculations based on
the Kompaneets operator. We solve the radiation transfer equation together with
the hydrostatic equilibrium equation accounting exactly for the radiation
pressure by electron scattering. We thus construct a new set of plane-parallel
atmosphere models in LTE for hot NSs. The models were computed for six chemical
compositions (pure H, pure He, solar H/He mix with various heavy elements
abundances Z = 1, 0.3, 0.1, and 0.01 Z_sun, and three log g = 14.0, 14.3, and
14.6. For each chemical composition and log g, we compute more than 26 model
atmospheres with various luminosities relative to the Eddington luminosity
L_Edd computed for the Thomson cross-section. The maximum relative luminosities
L/L_Edd reach values of up to 1.1 for high gravity models. The emergent spectra
of all models are redshifted and fitted by diluted blackbody spectra in the
3--20 keV energy range appropriate for the RXTE/PCA. We also compute the color
correction factors f_c. The radiative acceleration g_rad in our luminous,
hot-atmosphere models is significantly smaller than in corresponding models
based on the Kompaneets operator, because of the Klein-Nishina reduction of the
electron scattering cross-section, and therefore formally "super-Eddington"
model atmospheres do exist. The differences between the new and old model
atmospheres are small for L / L_Edd < 0.8. For the same g_rad / g, the new f_c
are slightly larger (by approximately 1%) than the old values.
Theoretical spectra of X-ray bursting neutron star (NS) model atmospheres are
widely used to determine the basic NS parameters such as their masses and
radii. We construct accurate NS atmosphere models using for the first time an
exact treatment of Compton scattering via the integral relativistic kinetic
equation. We also compare the results with the previous calculations based on
the Kompaneets operator. We solve the radiation transfer equation together with
the hydrostatic equilibrium equation accounting exactly for the radiation
pressure by electron scattering. We thus construct a new set of plane-parallel
atmosphere models in LTE for hot NSs. The models were computed for six chemical
compositions (pure H, pure He, solar H/He mix with various heavy elements
abundances Z = 1, 0.3, 0.1, and 0.01 Z_sun, and three log g = 14.0, 14.3, and
14.6. For each chemical composition and log g, we compute more than 26 model
atmospheres with various luminosities relative to the Eddington luminosity
L_Edd computed for the Thomson cross-section. The maximum relative luminosities
L/L_Edd reach values of up to 1.1 for high gravity models. The emergent spectra
of all models are redshifted and fitted by diluted blackbody spectra in the
3--20 keV energy range appropriate for the RXTE/PCA. We also compute the color
correction factors f_c. The radiative acceleration g_rad in our luminous,
hot-atmosphere models is significantly smaller than in corresponding models
based on the Kompaneets operator, because of the Klein-Nishina reduction of the
electron scattering cross-section, and therefore formally "super-Eddington"
model atmospheres do exist. The differences between the new and old model
atmospheres are small for L / L_Edd < 0.8. For the same g_rad / g, the new f_c
are slightly larger (by approximately 1%) than the old values.
Constraints on the gamma-ray emission from the cluster-scale AGN outburst in the Hydra A galaxy cluster. (arXiv:1208.1370v1 [astro-ph.CO])
Constraints on the gamma-ray emission from the cluster-scale AGN outburst in the Hydra A galaxy cluster. (arXiv:1208.1370v1 [astro-ph.CO]):
In some galaxy clusters powerful AGN have blown bubbles with cluster scale
extent into the ambient medium. The main pressure support of these bubbles is
not known to date, but cosmic rays are a viable possibility. For such a
scenario copious gamma-ray emission is expected as a tracer of cosmic rays from
these systems. Hydra A, the closest galaxy cluster hosting a cluster scale AGN
outburst, located at a redshift of 0.0538, is investigated for being a
gamma-ray emitter with the High Energy Stereoscopic System (H.E.S.S.) array and
the Fermi Large Area Telescope (Fermi-LAT). Data obtained in 20.2 hours of
dedicated H.E.S.S. observations and 38 months of Fermi-LAT data, gathered by
its usual all-sky scanning mode, have been analyzed to search for a gamma-ray
signal. No signal has been found in either data set. Upper limits on the
gamma-ray flux are derived and are compared to models. These are the first
limits on gamma-ray emission ever presented for galaxy clusters hosting cluster
scale AGN outbursts. The non-detection of Hydra A in gamma-rays has important
implications on the particle populations and physical conditions inside the
bubbles in this system. For the case of bubbles mainly supported by hadronic
cosmic rays, the most favorable scenario, that involves full mixing between
cosmic rays and embedding medium, can be excluded. However, hadronic cosmic
rays still remain a viable pressure support agent to sustain the bubbles
against the thermal pressure of the ambient medium. The largest population of
highly-energetic electrons which are relevant for inverse-Compton gamma-ray
production is found in the youngest inner lobes of Hydra A. The limit on the
inverse-Compton gamma-ray flux excludes a magnetic field below half of the
equipartition value of 16 muG in the inner lobes.
In some galaxy clusters powerful AGN have blown bubbles with cluster scale
extent into the ambient medium. The main pressure support of these bubbles is
not known to date, but cosmic rays are a viable possibility. For such a
scenario copious gamma-ray emission is expected as a tracer of cosmic rays from
these systems. Hydra A, the closest galaxy cluster hosting a cluster scale AGN
outburst, located at a redshift of 0.0538, is investigated for being a
gamma-ray emitter with the High Energy Stereoscopic System (H.E.S.S.) array and
the Fermi Large Area Telescope (Fermi-LAT). Data obtained in 20.2 hours of
dedicated H.E.S.S. observations and 38 months of Fermi-LAT data, gathered by
its usual all-sky scanning mode, have been analyzed to search for a gamma-ray
signal. No signal has been found in either data set. Upper limits on the
gamma-ray flux are derived and are compared to models. These are the first
limits on gamma-ray emission ever presented for galaxy clusters hosting cluster
scale AGN outbursts. The non-detection of Hydra A in gamma-rays has important
implications on the particle populations and physical conditions inside the
bubbles in this system. For the case of bubbles mainly supported by hadronic
cosmic rays, the most favorable scenario, that involves full mixing between
cosmic rays and embedding medium, can be excluded. However, hadronic cosmic
rays still remain a viable pressure support agent to sustain the bubbles
against the thermal pressure of the ambient medium. The largest population of
highly-energetic electrons which are relevant for inverse-Compton gamma-ray
production is found in the youngest inner lobes of Hydra A. The limit on the
inverse-Compton gamma-ray flux excludes a magnetic field below half of the
equipartition value of 16 muG in the inner lobes.
Friday, August 3, 2012
Origin of the X-ray disc-reflection steep radial emissivity. (arXiv:1208.0360v1 [astro-ph.HE])
Origin of the X-ray disc-reflection steep radial emissivity. (arXiv:1208.0360v1 [astro-ph.HE]):
X-ray reflection off the accretion disc surrounding a black hole, together
with the associated broad iron K$\alpha$ line, has been widely used to
constrain the innermost accretion-flow geometry and black hole spin. Some
recent measurements have revealed steep reflection emissivity profiles in a
number of active galactic nuclei and X-ray binaries. We explore the physically
motivated conditions that give rise to the observed steep disc-reflection
emissivity profiles. We perform a set of simulations based on the configuration
of a possible future high-resolution X-ray mission. Computations are carried
out for typical X-ray bright Seyfert-1 galaxies. We find that steep emissivity
profiles with $q\sim 4-5$ (where the emissivity is $\epsilon (r) \propto
r^{-q}$) are produced considering either i) a lamp-post scenario where a
primary compact X-ray source is located close to the black hole, or ii) the
radial dependence of the disc ionisation state. We also highlight the role of
the reflection angular emissivity: the radial emissivity index $q$ is
overestimated when the standard limb-darkening law is used to describe the
data. Very steep emissivity profiles with $q \geq 7$ are naturally obtained by
applying reflection models that take into account radial profile $\xi (r)$ of
the disc ionisation induced by a compact X-ray source located close to the
central black hole.
X-ray reflection off the accretion disc surrounding a black hole, together
with the associated broad iron K$\alpha$ line, has been widely used to
constrain the innermost accretion-flow geometry and black hole spin. Some
recent measurements have revealed steep reflection emissivity profiles in a
number of active galactic nuclei and X-ray binaries. We explore the physically
motivated conditions that give rise to the observed steep disc-reflection
emissivity profiles. We perform a set of simulations based on the configuration
of a possible future high-resolution X-ray mission. Computations are carried
out for typical X-ray bright Seyfert-1 galaxies. We find that steep emissivity
profiles with $q\sim 4-5$ (where the emissivity is $\epsilon (r) \propto
r^{-q}$) are produced considering either i) a lamp-post scenario where a
primary compact X-ray source is located close to the black hole, or ii) the
radial dependence of the disc ionisation state. We also highlight the role of
the reflection angular emissivity: the radial emissivity index $q$ is
overestimated when the standard limb-darkening law is used to describe the
data. Very steep emissivity profiles with $q \geq 7$ are naturally obtained by
applying reflection models that take into account radial profile $\xi (r)$ of
the disc ionisation induced by a compact X-ray source located close to the
central black hole.
Thermodynamical description of hadron-quark phase transition and its implications on compact-star phenomena. (arXiv:1208.0427v1 [astro-ph.HE])
Thermodynamical description of hadron-quark phase transition and its implications on compact-star phenomena. (arXiv:1208.0427v1 [astro-ph.HE]):
One of the most promising possibilities may be the appearance of quark matter
in astrophysical phenomena in the light of recent progress in observations. The
mechanism of deconfinement is not well understood, but the thermodynamical
aspects of the hadron-quark (HQ) phase transition have been extensively studied
in recent years. Then the mixed phase of hadron and quark matter becomes
important; the proper treatment is needed to describe the HQ phase transition
and derive the equation of state (EOS) for the HQ matter, based on the Gibbs
conditions for phase equilibrium. We here adopt a EOS based on the
baryon-baryon interactions including hyperons for the hadron phase, while we
use rather simple EOS within the MIT bag model in the quark phase. For quark
matter we further try to improve the previous EOS by considering other
effective models of QCD. One of the interesting consequences may be the
appearance of the inhomogeneous structures called "pasta", which are brought
about by the surface and the Coulomb interaction effects. We present here a
comprehensive review of our recent works about the HQ phase transition in
various astrophysical situations: cold catalyzed matter, hot matter and
neutrino-trapped matter. We show how the pasta structure becomes unstable by
the charge screening of the Coulomb interaction, thermal effect or the neutrino
trapping effect. Such inhomogeneous structure may affect astrophysical
phenomena through its elasticity or thermal properties. Here we also discuss
some implications on supernova explosion, gravitational wave and cooling of
compact stars.
One of the most promising possibilities may be the appearance of quark matter
in astrophysical phenomena in the light of recent progress in observations. The
mechanism of deconfinement is not well understood, but the thermodynamical
aspects of the hadron-quark (HQ) phase transition have been extensively studied
in recent years. Then the mixed phase of hadron and quark matter becomes
important; the proper treatment is needed to describe the HQ phase transition
and derive the equation of state (EOS) for the HQ matter, based on the Gibbs
conditions for phase equilibrium. We here adopt a EOS based on the
baryon-baryon interactions including hyperons for the hadron phase, while we
use rather simple EOS within the MIT bag model in the quark phase. For quark
matter we further try to improve the previous EOS by considering other
effective models of QCD. One of the interesting consequences may be the
appearance of the inhomogeneous structures called "pasta", which are brought
about by the surface and the Coulomb interaction effects. We present here a
comprehensive review of our recent works about the HQ phase transition in
various astrophysical situations: cold catalyzed matter, hot matter and
neutrino-trapped matter. We show how the pasta structure becomes unstable by
the charge screening of the Coulomb interaction, thermal effect or the neutrino
trapping effect. Such inhomogeneous structure may affect astrophysical
phenomena through its elasticity or thermal properties. Here we also discuss
some implications on supernova explosion, gravitational wave and cooling of
compact stars.
Wednesday, August 1, 2012
Quasar feedback: accelerated star formation and chaotic accretion. (arXiv:1207.7200v1 [astro-ph.CO])
Quasar feedback: accelerated star formation and chaotic accretion. (arXiv:1207.7200v1 [astro-ph.CO]):
Growing Supermassive Black Holes (SMBH) are believed to influence their
parent galaxies in a negative way, terminating their growth by ejecting gas out
before it could turn into stars. Here we present some of the most sophisticated
SMBH feedback simulations to date showing that quasar's effects on galaxies are
not always negative. We find that when the ambient shocked gas cools rapidly,
the shocked gas is compressed into thin cold dense shells, filaments and
clumps. Driving these high density features out is much more difficult than
analytical models predict since dense filaments are resilient to the feedback.
However, in this regime quasars have another way of affecting the host -- by
triggering a massive star formation burst in the cold gas by over-pressurising
it. Under these conditions SMBHs actually accelerate star formation in the
host, having a positive rather than negative effect on their host galaxies. The
relationship between SMBH and galaxies is thus even more complex and symbiotic
than currently believed. We also suggest that the instabilities found here may
encourage the chaotic AGN feeding mode.
Growing Supermassive Black Holes (SMBH) are believed to influence their
parent galaxies in a negative way, terminating their growth by ejecting gas out
before it could turn into stars. Here we present some of the most sophisticated
SMBH feedback simulations to date showing that quasar's effects on galaxies are
not always negative. We find that when the ambient shocked gas cools rapidly,
the shocked gas is compressed into thin cold dense shells, filaments and
clumps. Driving these high density features out is much more difficult than
analytical models predict since dense filaments are resilient to the feedback.
However, in this regime quasars have another way of affecting the host -- by
triggering a massive star formation burst in the cold gas by over-pressurising
it. Under these conditions SMBHs actually accelerate star formation in the
host, having a positive rather than negative effect on their host galaxies. The
relationship between SMBH and galaxies is thus even more complex and symbiotic
than currently believed. We also suggest that the instabilities found here may
encourage the chaotic AGN feeding mode.
Synthetic X-ray spectra for simulations of the dynamics of an accretion flow irradiated by a quasar. (arXiv:1207.7194v1 [astro-ph.HE])
Synthetic X-ray spectra for simulations of the dynamics of an accretion flow irradiated by a quasar. (arXiv:1207.7194v1 [astro-ph.HE]):
Ultraviolet and X-ray observations show evidence of outflowing gas around
many active galactic nuclei. Some of these outflows may be driven off gas
infalling towards the central black hole. We perform radiative transfer
calculations to compute the gas ionization state and X-ray spectra for two- and
three-dimensional (3D) hydrodynamical simulations of this outflow-from-inflow
scenario. By comparison with observations, our results can be used to test the
theoretical models and guide future numerical simulations. We predict both
absorption and emission features, most of which are formed in a polar funnel of
outflowing gas. This outflow causes strong absorption for observer orientation
angles of < 35 degrees. Particularly in 3D, the strength of this absorption
varies significantly for different lines-of-sight owing to the fragmentary
structure of the gas flow. Although infalling material occupies a large
fraction of the simulation volume, we do not find that it imprints strong
absorption features since the ionization state is very high. Thus, an absence
of observed inflow absorption features does not exclude the models. The main
spectroscopic consequence of the infalling gas is a scattered continuum
component that partially re-fills the absorption features caused by the
outflowing polar funnel. Fluorescence and scattering in the outflow is
predicted to give rise to several emission features for all observer
orientations. For the hydrodynamical simulations considered we find both
ionization states and column densities for the outflowing gas that are too high
to be quantitatively consistent with well-observed X-ray absorption systems.
Nevertheless, our results are qualitatively encouraging and further exploration
of the model parameter space is warranted. (Abridged.)
Ultraviolet and X-ray observations show evidence of outflowing gas around
many active galactic nuclei. Some of these outflows may be driven off gas
infalling towards the central black hole. We perform radiative transfer
calculations to compute the gas ionization state and X-ray spectra for two- and
three-dimensional (3D) hydrodynamical simulations of this outflow-from-inflow
scenario. By comparison with observations, our results can be used to test the
theoretical models and guide future numerical simulations. We predict both
absorption and emission features, most of which are formed in a polar funnel of
outflowing gas. This outflow causes strong absorption for observer orientation
angles of < 35 degrees. Particularly in 3D, the strength of this absorption
varies significantly for different lines-of-sight owing to the fragmentary
structure of the gas flow. Although infalling material occupies a large
fraction of the simulation volume, we do not find that it imprints strong
absorption features since the ionization state is very high. Thus, an absence
of observed inflow absorption features does not exclude the models. The main
spectroscopic consequence of the infalling gas is a scattered continuum
component that partially re-fills the absorption features caused by the
outflowing polar funnel. Fluorescence and scattering in the outflow is
predicted to give rise to several emission features for all observer
orientations. For the hydrodynamical simulations considered we find both
ionization states and column densities for the outflowing gas that are too high
to be quantitatively consistent with well-observed X-ray absorption systems.
Nevertheless, our results are qualitatively encouraging and further exploration
of the model parameter space is warranted. (Abridged.)
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