Related papers: Modeling the Time Variability of Black Hole Candid…
Black hole accretion flows show rapid X-ray variability. The Power Spectral Density (PSD) of this is typically fit by a phenomenological model of multiple Lorentzians for both the broad band noise and Quasi-Periodic Oscillations (QPOs). Our…
We present results from a 20 ksec RXTE observation of the black hole candidate Cyg X-1. We apply self-consistent accretion disk corona models to these hard state data and show that Comptonization in a spherical corona irradiated by soft…
We have performed Monte Carlo simulations of Compton upscattering of low-energy photons in an accretion disk around a Schwarzschild black hole. The photons gain energy from the rotational motion of the electrons in the disk. The…
The quasi-symmetric shape of the lightcurves, as seen in the X-rays and in the optical, together with the fast variations of the flux observed, suggest that the cooling time for the highest energy electrons may be shorter than the light…
We study the spectra generated as a result of bulk Comptonization by relativistic electrons in radial flows onto compact objects. We solve numerically the general-relativistic radiative transfer equation in the Schwarzschild spacetime, in…
Blazars show variability on timescales ranging from minutes to years, the former being comparable to and in some cases even shorter than the light-crossing time of the central black hole. The observed gamma-ray lightcurves can be described…
We present a model for the short timescale spectral variability of accreting black holes. It describes well the time-averaged spectra as well as temporal characteristics such as power-density spectrum, time/phase lags, and coherence…
We present the results of several numerical simulations of two dimensional axi-symmetric accretion flows around black holes using Smoothed Particle Hydrodynamics (SPH) in the presence of cooling effects. We consider both stellar black holes…
We model the spectral energy distribution of the type 1 Seyfert galaxies, fitting data from simultaneous optical, UV, and X-ray monitoring observations. We assume a geometry consisting of a hot central Comptonizing region surrounded by a…
Universal to black hole X-ray binaries, the high-frequency soft lag gets longer during the hard-to-intermediate state transition, evolving from ${\lesssim}1~{\rm ms}$ to ${\sim}10~{\rm ms}$. The soft lag production mechanism is thermal disk…
Theory of random processes provides an attractive mathematical tool to describe the fluctuating signal from accreting sources, such as active galactic nuclei and Galactic black holes observed in X-rays. These objects exhibit featureless…
We extract the spectra of the fastest variability (above 10 Hz) from the black hole XTE J1550-564 during a transition from hard to soft state on the rise to outburst. We confirm previous results that the rapid variability contains no…
We use the XMM-Newton EPIC-pn instrument in timing mode to extend spectral time-lag studies of hard state black hole X-ray binaries into the soft X-ray band. We show that variations of the disc blackbody emission substantially lead…
we propose a jet model for the low/hard state of black-hole X-ray sources which explains a) the X-ray spectra, b) the timelag spectra, c) the increase in the amplitude (QPO and high frequency) with increasing photon energy, and d) the…
Black hole X-ray binaries in their hard and hard-intermediate states display hard and soft time lags between broadband noise variations (high-energy emission lagging low-energy and vice versa), which could be used to constrain the geometry…
Using the Rossi X-ray Timing Explorer we have measured lags of the 9 to 33 keV photons relative to the 2 to 9 keV photons in the timing noise between 0.01 and 100 Hz in the accreting neutron stars 4U 0614+091 and 4U 1705-44. We performed…
We analyze the exact general relativistic exact integro-differential equation of radiative transfer describing the interaction of low energy photons with a Maxwellian distribution of hot electrons in gravitational field of a Schwarzschild…
I review radiative processes responsible for X-ray emission in the hard (low) and soft (high) spectral states of black-hole binaries. The main process in the hard state appears to be thermal Comptonization (in a hot plasma) of blackbody…
The spectra of black hole binaries in the low/hard state are complex, with evidence for multiple different Comptonisation regions contributing to the hard X-rays in addition to a cool disc component. We show this explicitly for some of the…
We use long-run, high-resolution hydrodynamics simulations to compute the multi-wavelength light curves (LCs) from thermal disk emission around accreting equal-mass supermassive black hole (BH) binaries, with a focus on revealing binary…