67 research outputs found
New Evidence for a Black Hole in the Compact Binary Cygnus X-3
The bright and highly variable X-ray and radio source known as Cygnus X-3 was
among the first X-ray sources discovered, yet it remains in many ways an
enigma. Its known to consist of a massive, Wolf-Rayet primary in an extremely
tight orbit with a compact object. Yet one of the most basic of parameters -
the mass of the compact object - is not known. Nor is it even clear whether its
is a neutron star or a black hole. In this Paper we present our analysis of the
broad-band high-energy continua covering a substantial range in luminosity and
spectral morphology. We apply these results to a recently identified scaling
relationship which has been demonstrated to provide reliable estimates of the
compact object mass in a number of accretion powered binaries. This analysis
leads us to conclude that the compact object in Cygnus X-3 has a mass greater
than thus clearly indicative of a black hole and as such resolving
a long-standing issue. The full range of uncertainty in our analysis and from
using a range of recently published distance estimates constrains the compact
object mass to lie between and . Our favored
estimate, based on a 9.0 kpc distance estimate is with the
error margin of 3.2 solar masses. This result may thus pose challenges to
shared-envelope evolutionary models of compact binaries, as well as
establishing Cygnus X-3 as the first confirmed accretion-powered galactic
gamma-ray source
Gamma-Ray Emission from X-Ray Binaries
We summarize the current observational picture regarding high-energy emission from Galactic X-ray binaries, reviewing the results of the Compton Gamma Ray Observatory mission. We speculate on the prospects for the GLAST era
Downscattering due to Wind Outflows in Compact X-ray Sources: Theory and Interpretation
A number of recent lines of evidence point towards the presence of hot,
out-flowing plasma from the central regions of compact Galactic and
extragalactic X-ray sources. Additionally, it has long been noted that many of
these sources exhibit an ``excess'' continuum component, above 10 keV, usually
attributed to Compton Reflection from a static medium. Motivated by these
facts, as well as by recent observational constraints on the Compton reflection
models - specifically apparently discrepant variability timescales for line and
continuum components in some cases -- we consider possible effects of
out-flowing plasma on the high-energy continuum spectra of accretion powered
compact objects. We present a general formulation for photon downscattering
diffusion which includes recoil and Comptonization effects due to divergence of
the flow. We then develop an analytical theory for the spectral formation in
such systems that allows us to derive formulae for the emergent spectrum.
Finally we perform the analytical model fitting on several Galactic X-ray
binaries. Objects which have been modeled with high-covering-fraction Compton
reflectors, such as GS1353-64 are included in our analysis. In addition, Cyg
X-3, is which is widely believed to be characterized by dense circumstellar
winds with temperature of order 10^6 K, provides an interesting test case. Data
from INTEGRAL and RXTE covering the 3-300 keV range are used in our analysis.
We further consider the possibility that the widely noted distortion of the
power-law continuum above 10 keV may in some cases be explained by these
spectral softening effects.Comment: 16 pages, 5 figures, accepted for publication in the Astrophysical
Journal and scheduled for 1 December 2004, vol 616 issu
IUE and ROSAT monitoring of the bright QSO H1821+643
The analysis is presented of IUE observations of the bright QSO H1821+643, obtained during the ROSAT All Sky Survey (the RIASS program). The objectives were: (1) to establish whether the UV and soft X ray radiation have the same physical origin; and (2) to determine if this physical origin is an accretion disk. Supporting ground based spectrophotometry was also obtained. The analysis shows that the shape and flux level of the UV continuum did not vary among the seven IUE observation spanning one month, to an upper limit of about 8 percent. So it is of great interest to determine whether the soft X ray flux varied during this period. Since X ray variability in AGNs is often more rapid and of higher amplitude than in the UV, detection of X ray variability in the ROSAT data could severely challenge the accretion disk model for the soft X ray excess
Toward a Unified AGN Structure
We present a unified model for the structure and appearance of accretion
powered sources across their entire luminosity range from galactic X-ray
binaries to luminous quasars, with emphasis on AGN and their phenomenology.
Central to this model is the notion of MHD winds launched from the accretion
disks that power these objects. These winds provide the matter that manifests
as blueshifted absorption features in the UV and X-ray spectra of a large
fraction of these sources; furthermore, their density distribution in the
poloidal plane determines the "appearance" (i.e. the column and velocity
structure of these absorption features) as a function of the observer
inclination angle. This work focuses on just the broadest characteristics of
these objects; nonetheless, it provides scaling laws that allow one to
reproduce within this model the properties of objects spanning a very wide
luminosity range and viewed at different inclination angles, and trace them to
a common underlying dynamical structure. Its general conclusion is that the AGN
phenomenology can be accounted for in terms of three parameters: The wind mass
flux in units of the Eddington value, , the observer's inclination
angle and the logarithmic slope between the O/UV and X-ray fluxes
. However, because of a significant correlation between
and UV luminosity, we conclude that the AGN structure depends on
only two parameters. Interestingly, the correlations implied by this model
appear to extend to and consistent with the characteristics of galactic X-ray
sources, suggesting the presence of a truly unified underlying structure for
accretion powered sources.Comment: submitted to the Astronomical Review, 32pg, 8 fig
Do the Spectra of Soft X-ray Transients Reveal Bulk Motion Inflow Phenomenon?
We present our analysis of the high-energy radiation from black hole (BH)
transients, using archival data obtained primarily with RXTE observatory, and a
comprehensive test of the bulk motion Comptonization (BMC) model for the
high-soft state continuum. The emergent spectra of over 30 separate
measurements of GRO J1655-40, GRS 1915+105, GRS 1739-278, 4U 1630-47 XTE
J1755-32, and EXO~1846-031 X-ray sources are successfully fitted by the BMC
model, which has been derived from basic physical principles in previous work.
This in turn provides direct physical insight into the innermost observable
regions where matter impinging upon the event horizon can effectively be
directly viewed. The BMC model is characterized by three parameters: the disk
color temperature, a geometric factor related to the illumination of the black
hole (BH) site by the disk and a spectral index related to the efficiency of
the bulk motion upscattering. For the case of GRO J1655-40, where there are
distance and mass determinations, a self consistency check of the BMC model has
been made. Using model parameters we present new, independent constraints on
the black hole mass, mass accretion rate and the distance for the
aforementioned sources. Notable is the relationship between the color
temperature and flux, which for GRO J1655-40 is entirely distinct from a simple
T^4 dependence, and consistent with the disk model we have invoked - standard
Shakura-Sunyaev's disk. This allows us to impose an important estimation of the
hardness parameter, the ratio of the color temperature to the effective
temperature - we find T_h~2.6, higher than previous estimates used in the
literature.Comment: 50 pages, 8 figures, accepted for publication in the Astrophysical
Journal (scheduled for the May 20, 1999 issue
Stratified Magnetically-Driven Accretion-Disk Winds and Their Relations to Jets
We explore the poloidal structure of two-dimensional (2D) MHD winds in
relation to their potential association with the X-ray warm absorbers (WAs) and
the highly-ionized ultra-fast outflows (UFOs) in AGN, in a single unifying
approach. We present the density , ionization parameter
, and velocity structure of such ionized winds for
typical values of their fluid-to-magnetic flux ratio, , and specific angular
momentum, , for which wind solutions become super-\Alfvenic. We explore the
geometrical shape of winds for different values of these parameters and
delineate the values that produce the widest and narrowest opening angles of
these winds, quantities necessary in the determination of the statistics of AGN
obscuration. We find that winds with smaller show a poloidal geometry of
narrower opening angles with their \Alfven\ surface at lower inclination angles
and therefore they produce the highest line of sight (LoS) velocities for
observers at higher latitudes with the respect to the disk plane. We further
note a physical and spatial correlation between the X-ray WAs and UFOs that
form along the same LoS to the observer but at different radii, , and
distinct values of , and consistent with the latest spectroscopic
data of radio-quiet Seyfert galaxies. We also show that, at least in the case
of 3C 111, the winds' pressure is sufficient to contain the relativistic plasma
responsible for its radio emission. Stratified MHD disk-winds could therefore
serve as a unique means to understand and unify the diverse AGN outflows.Comment: version 2 (modified), 27 pages, 5 figures, accepted to Ap
Magnetically-Driven Accretion-Disk Winds and Ultra-Fast Outflows in PG1211+143
We present a study of X-ray ionization of magnetohydrodynamic (MHD)
accretion-disk winds in an effort to constrain the physics underlying the
highly-ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often
detected in various sub-classes of Seyfert active galactic nuclei (AGNs). Our
primary focus is to show that magnetically-driven outflows are indeed
physically plausible candidates for the observed outflows accounting for the
AGN absorption properties of the present X-ray spectroscopic observations.
Employing a stratified MHD wind launched across the entire AGN accretion disk,
we calculate its X-ray ionization and the ensuing X-ray absorption line
spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds
to model the absorption features in an {\it XMM-Newton}/EPIC spectrum of the
narrow-line Seyfert, \pg. We find, through identifying the detected features
with Fe K transitions, that the absorber has a characteristic
ionization parameter of ^{-1} and a
column density on the order of cm, outflowing at a
characteristic velocity of (where is the speed of
light). The best-fit model favors its radial location at
( is the black hole innermost stable circular orbit), with an inner wind
truncation radius at . The overall K-shell feature in
the data is suggested to be dominated by \fexxv\ with very little contribution
from \fexxvi\ and weakly-ionized iron, which is in a good agreement with a
series of earlier analysis of the UFOs in various AGNs including \pg.Comment: v.3 as of 5/6/15 with eliminating extra figs: accepted to ApJ, 28
pages, figs.1-6 (color), 3 table
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