140 research outputs found
A two zone model for the broad Iron line emission in MCG-6-30-15
We reanalyze the ASCA and BeppoSAX data of MCG-6-30-15, using a double zone
model for the Iron line profile. In this model, the X-ray source is located
around Schwarzschild radius and the regions interior and exterior
to the X-ray source produce the line emission. We find that this model fits the
data with similar reduced as the standard single zone model. The best
fit inclination angle of the source () for the medium intensity
ASCA data set is compatible with that determined by earlier modeling of optical
lines. The observed variability of the line profile with intensity can be
explained as variations of the X-ray source size. That several AGN with broad
lines have the peak centroid near 6.4 keV can be explained within the framework
of this model under certain conditions.
We also show that the simultaneous broad band observations of this source by
BeppoSAX rules out the Comptonization model which was an alternative to the
standard inner disk one. We thereby strengthen the case that the line
broadening occurs due to the strong gravitational influence of a Black Hole.Comment: submitted to mnra
A Self-Consistent Model For The Long-Term Gamma-Ray Spectral Variability of Cygnus X-1
The long-term transitions of the black hole candidate Cygnus X-1 (between the
states gamma_1, gamma_2, and gamma_3) include the occasional appearance of a
strong ~ MeV bump (gamma_1), whose strength appears to be anti-correlated with
the continuum flux (~ 400 keV) due to the Compton upscattering of cold disk
photons by the inner, hot corona. We develop a self-consistent disk picture
that accounts naturally for these transitions and their corresponding spectral
variations. We argue that the bump is due to the self-Comptonization of
bremsstrahlung photons emitted predominantly near the plane of the corona
itself. Our results suggest that a decrease by a factor of approx 2 in the
viscosity parameter alpha is responsible for quenching this bump and driving
the system to the gamma_2 state, whereas a transition from gamma_2 to gamma_3
appears to be induced by an increase of about 25 % in the accretion rate Mdot.
In view of the fact that most of the transitions observed in this source seem
to be of the gamma_2 to gamma_3 variety, we conclude that much of the long term
gamma-ray spectral variability in Cygnus X-1 is due to these small fluctuations
in Mdot. The unusual appearance of the gamma_1 state apparently reflects a
change in the dissipative processes within the disk.Comment: 13 pages, Plain TeX, (Steward Preprint
Long-term Spectral Variability of the Ultra-luminous X-ray source Holmberg IX X--1
We investigate the long-term spectral variability in the ultra-luminous X-ray
source Holmberg IX X--1. By analyzing the data from eight {\it Suzaku} and 13
{\it XMM-Newton} observations conducted between 2001 and 2015, we perform a
detailed spectral modeling for all spectra with simple models and complex
physical models. We find that the spectra can be well explained by a disc plus
thermal Comptonization model. Applying this model, we unveil correlations
between the X-ray luminosity () and the spectral parameters. Among
the correlations, a particular one is the statistically significant positive
correlation between and the photon index (), while at the
high luminosities of , the source becomes
marginally hard and that results a change in the slope of the correlation. Similar variability behavior is observed in the optical depth
of the source around as the
source becomes more optically thick. We consider the scenario that a corona
covers the inner part of the disc, and the correlations can be explained as to
be driven by the variability of seed photons from the disc input into the
corona. On the basis of the disc-corona model, we discuss the physical
processes that are possibly indicated by the variability of the spectral
parameters. Our analysis reveals the complex variability behavior of Holmberg
IX X--1 and the variability mechanism is likely related to the geometry of the
X-ray emitting regions.Comment: Accepted for publication in ApJ, 12 Pages, 3 Tables, 3 Figure
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