Related papers: Self-Consistent Thermal Accretion Disk Corona Mode…
(truncated version) The X-ray spectra of Galactic binary systems in the very high state show both strong disk emission and a strong, steep tail to high energies. We use simultaneous optical-ASCA-RXTE data from the black hole transient XTE…
Existence of relatively cool ($k_B T \lesssim 10~{\rm keV}$) and optically thick ($\tau \gtrsim 3$) coronae are inferred above super-Eddington accretion flow such as ultraluminous X-ray sources (ULXs), GRS 1915+105, and narrow-line Seyfert…
We observed the Galactic black hole Cygnus X-1 with the Chandra High Energy Transmission Grating Spectrometer for 30 kiloseconds on 4 January, 2001. The source was in an intermediate state, with a flux that was approximately twice that…
The characteristic timescale ($\tau$) of continuum variability of the accretion disk in active galactic nuclei (AGNs) is known to be related to the thermal timescale, which is predicted to scale with AGN luminosity ($L$) and restframe…
X-ray reverberation in AGN, believed to be the result of the reprocessing of corona photons by the underlying accretion disk, has allowed us to probe the properties of the inner-most regions of the accretion flow and the central black hole.…
We report estimates of the X-ray coronal size of active galactic nuclei in the lamppost geometry. In this commonly adopted scenario, the corona is assumed for simplicity to be a point-like X-ray source located on the axis of the accretion…
Popular models for the formation of X-ray spectra in AGN assume that a large fraction of the disk's angular momentum dissipation takes place in a hot corona that carries a small amount of the accreting mass. Here I discuss the formation of…
We present a comprehensive timing analysis of the black hole X-ray binary Cygnus X-1 using 26 NuSTAR observations spanning 2012-2024, providing the most detailed characterization to date of its accretion flow variability across spectral…
This paper is devoted to self-consistent modeling of the magnetically supported accretion disk with optically thick warm corona based on first principles. In our model, we consider the gas heating by magneto-rotational instability (MRI)…
We solve for the structure of a hot accretion disc with unsaturated thermal Comptonisation of soft photons and with advection, generalizing the classical model of Shapiro et al. The upper limit on the accretion rate due to advection…
Black hole X-ray binaries are ideal environments to study the accretion phenomena in strong gravitational potentials. These systems undergo dramatic accretion state transitions and analysis of the X-ray spectra is used to probe the…
The bulk of the X-ray emission in Active Galactic Nuclei (AGN) is produced very close to the accreting supermassive black hole (SMBH), in a corona of hot electrons which up scatters optical and ultraviolet photons from the accretion flow.…
In this work, we carry out a new spectral reanalysis of NuSTAR and Suzaku observations of the disk reflection spectra in the stellar-mass black hole X-ray binary Cyg~X-1. We compare three types of models: a broken power-law disk emissivity…
Aims. We investigate observations of the X-ray binary Cygnus X-1 with unusually high hardness and low flux. In particular, we study the characteristic frequencies seen in the PDS and the hardness-flux correlation within and between these…
We discuss properties of thermal and hybrid (thermal/non-thermal) electron-positron plasmas in the pair and energy equilibria. Various accretion disc-corona models, recently proposed to explain properties of galactic as well as…
We study vertical structure of radiation pressure dominated disc with a hot corona. We include all the relevant processes like bound--free opacity and convection. We show that the presence of the corona modifies considerably the density and…
We present models of the soft X-ray transients, A0620-00, V404 Cyg, and X-ray Nova Mus 1991, in quiescence. In each source, we postulate that there is an outer region, extending outward from about 3000 Schwarzschild radii, where the…
We use time domain analysis techniques to investigate the rapid variability of Cygnus X-1. We show that the cross-correlation functions between hard and soft energy bands reach values very close to unity and peak at a lag of less than 2…
The microquasar Cygnus X-3 was detected at high energies by the gamma-ray space telescopes AGILE and Fermi. The gamma-ray emission is transient, modulated with the orbital period and seems related to major radio flares, i.e. to the…
We build a self-consistent model of a warm scattering corona near an accreting black hole in Kerr geometry, in the regime of slow ($\sim 0.01$ Eddington) mass accretion. An iterative Monte Carlo procedure is developed that incorporates…