325 research outputs found
Modelling the energy dependencies of high-frequency QPO in black hole X-ray binaries
We model energy dependencies of the quasi periodic oscillations (QPO) in the
model of disc epicyclic motions, with X-ray modulation caused by varying
relativistic effects. The model was proposed to explain the high frequency QPO
observed in X-ray binaries. We consider two specific scenarios for the geometry
of accretion flow and spectral formation. Firstly, a standard cold accretion
disc with an active X-ray emitting corona is assumed to oscillate. Secondly,
only a hot X-ray emitting accretion flow oscillates, while the cold disc is
absent at the QPO radius. We find that the QPO spectra are generally similar to
the spectrum of radiation emitted at the QPO radius, and they are broadened by
the relativistic effects. In particular, the QPO spectrum contains the disc
component in the oscillating disc with a corona scenario. We also review the
available data on energy dependencies of high frequency QPO, and we point out
that they appear to lack the disc component in their energy spectra. This would
suggest the hot flow geometry in the spectral states when high frequency QPO
are observed.Comment: 8 pages, accepted for publication in MNRA
X-ray observations of the hot phase in Sgr~A*
We analyze 134 ks Chandra ACIS-I observations of the Galactic Centre (GC)
performed in July 2011. The X-ray image with the field of view
contains the hot plasma surrounding the Sgr~A*. The obtained surface brightness
map allow us to fit Bondi hot accretion flow to the innermost hot plasma around
the GC. We have fitted spectra from region up to from Sgr~A* using a
thermal bremsstrahlung model and four Gaussian profiles responsible for
K emission lines of Fe, S, Ar, and Ca. The X-ray surface brightness
profile up to from Sgr~A* found in our data image, was successfully fitted
with the dynamical model of Bondi spherical accretion. By modelling the surface
brightness profile, we derived the temperature and number density profiles in
the vicinity of the black hole. The best fitted model of spherical Bondi
accretion shows that this type of flow works only up to and implies outer
plasma density and temperature to be:
cm and keV respectively. We show
that the Bondi flow can reproduce observed surface brightness profile up to
from Sgr~A* in the Galactic Center. This result strongly suggests the
position of stagnation radius in the complicated dynamics around GC. The
Faraday rotation computed from our model towards the pulsar PSR J1745-2900 near
the GC agrees with the observed one, recently reported.Comment: 10 pages, 7 figures, accepted for publication in A&
Energy spectra of X-ray quasi-periodic oscillations in accreting black hole binaries
We investigate the energy dependencies of X-ray quasi-periodic oscillations
in black hole X-ray binaries. We analyze RXTE data on both the low- and
high-frequency QPO. We construct the low-f QPO energy spectra, and demonstrate
that they do not contain the thermal disk component, even though the latter is
present in the time averaged spectra. The disk thus does not seem to
participate in the oscillations. Moreover the QPO spectra are harder than the
time averaged spectra when the latter are soft, which can be modeled as a
result of modulations occurring in the hot plasma. The QPO spectra are softer
than the time averaged spectra when the latter are hard. The absence of the
disk component in the QPO spectra is true also for the high-frequency
(hecto-Hz) QPO observed in black hole binaries. We compute the QPO spectra
expected from the model of disk resonances.Comment: 4 pages, Proc. of IAU Symposium 238, "Black Holes from Stars to
Galaxies - across the range of masses", Prague, Aug 200
Testing wind as an explanation for the spin problem in the continuum-fitting method
The continuum-fitting method is one of the two most advanced methods of
determining the black hole spin in accreting X-ray binary systems. There are,
however, still some unresolved issues with the underlying disk models. One of
them manifests as an apparent decrease in spin for increasing source
luminosity. Here, we perform a few simple tests to establish whether outflows
from the disk close to the inner radius can address this problem. We employ
four different parametric models to describe the wind and compare these to the
apparent decrease in spin with luminosity measured in the sources LMC~X-3 and
GRS~1915+105. Wind models in which parameters do not explicitly depend on the
accretion rate cannot reproduce the spin measurements. Models with mass
accretion rate dependent outflows, however, have spectra that emulate the
observed ones. The assumption of a wind thus effectively removes the artifact
of spin decrease. This solution is not unique; the same conclusion can be
obtained with a truncated inner disk model. To distinguish among valid models,
high resolution X-ray data and a realistic description of the Comptonization in
the wind will be needed.Comment: 14 pages, 11 figures, accepted by Ap
The X-ray Energy Dependence of the Relation between Optical and X-ray Emission in Quasars
We develop a new approach to the well-studied anti-correlation between the
optical-to-X-ray spectral index, alpha_ox, and the monochromatic optical
luminosity, l_opt. By cross-correlating the SDSS DR5 quasar catalog with the
XMM-Newton archive, we create a sample of 327 quasars with X-ray S/N > 6, where
both optical and X-ray spectra are available. This allows alpha_ox to be
defined at arbitrary frequencies, rather than the standard 2500 Angstroms and 2
keV. We find that while the choice of optical wavelength does not strongly
influence the alpha_ox-l_opt relation, the slope of the relation does depend on
the choice of X-ray energy. The slope of the relation becomes steeper when
alpha_ox is defined at low (~ 1 keV) X-ray energies. This change is significant
when compared to the slope predicted by a decrease in the baseline over which
alpha_ox is defined. The slopes are also marginally flatter than predicted at
high (~ 10 keV) X-ray energies. Partial correlation tests show that while the
primary driver of alpha_ox is l_opt, the Eddington ratio correlates strongly
with alpha_ox when l_opt is taken into account, so accretion rate may help
explain these results. We combine the alpha_ox-l_opt and Gamma -L_bol/L_Edd
relations to naturally explain two results: 1) the existence of the Gamma-l_x
relation as reported in Young et al. (2009) and 2) the lack of a Gamma-l_opt
relation. The consistency of the optical/X-ray correlations establishes a more
complete framework for understanding the relation between quasar emission
mechanisms. We also discuss two correlations with the hard X-ray bolometric
correction, which we show correlates with both alpha_ox and Eddington ratio.
This confirms that an increase in accretion rate correlates with a decrease in
the fraction of up-scattered disk photons.Comment: 27 pages preprint style, 10 figures. New material added to section
4.3 (Fig. 11) regarding hard X-ray bolometric corrections. Accepted for
publication in Astrophysical Journa
Synthetic catalog of black holes in the Milky Way
We present an open-access database which includes a synthetic catalog of
black holes in the Milky Way. To calculate evolution of single and binary stars
we used updated population synthesis code StarTrack. We applied a new model of
star formation history and chemical evolution of Galactic disk, bulge and halo
synthesized from observational and theoretical data. We find that at the
current moment Milky Way (disk+bulge+halo) contains about 1.2 x 10^8 single
black holes with average mass of about 14 Msun and 9.3 x 10^6 BHs in binary
systems with average mass of 19 Msun. We present basic statistical properties
of BH populations such as distributions of single and binary BH masses,
velocities, orbital parameters or numbers of BH binary systems in different
evolutionary configurations. We find that the most massive BHs are formed in
mergers of binary systems, such as BH-MS, BH+He, BH-BH. The metallicity of
stellar population has a significant impact on the final BH mass due to the
stellar winds. Therefore the most massive single BH in our simulation, 113
Msun, originates from a merger of a helium star and a black hole in a low
metallicity stellar environment in Galactic halo. The most massive BH in binary
system is 60 Msun and was also formed in Galactic halo. We constrain that only
0.006% of total Galactic halo mass (including dark matter) could be hidden in
the form of stellar origin BHs which are not detectable by current
observational surveys. Galactic binary BHs are minority (10% of all Galactic
BHs) and most of them are in BH-BH systems. The current Galactic merger rates
for two considered common envelope models which are: 3-81 Myr^-1 for BH-BH, 1-9
Myr^-1, for BH-NS and 14-59 Myr^-1 for NS-NS systems. Data files are available
at https://bhc.syntheticuniverse.org/.Comment: 21 pages, A&A accepted, data from catalog available onlin
Commutative reduced filial rings
A ring R is filial when for every I, J, if I is an ideal of J and J is an ideal of R then I is an ideal of R. Several characterizations and results on structure of commutative reduced filial rings are obtained
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