Related papers: X-ray spectral states of microquasars
Energetic X-ray radiations emitted from various accretion systems are widely considered to be produced by Comptonization in the hot corona. The corona and its interaction with the disc play an essential role in the evolution of the system…
A new mechanism to form a magnetic pressure supported, high temperature corona above the photosphere of an accretion disk is explored using three dimensional radiation magneto-hydrodynamic (MHD) simulations. The thermal properties of the…
We analyse the spectra of black hole (BH) and neutron star (NS) X-ray binaries (XBs) in the hard state using archival RXTE observations. We find that there is a clear dichotomy in the strength of Comptonisation between NS and BH sources, as…
It is widely accepted that X-ray emission in luminous active galactic nuclei (AGNs) originates from hot corona. To prevent the corona from over-cooling by strong X-ray emission, steady heating to the corona is essential, for which the most…
We present the results of a new global radiation transport code coupled to a general relativistic magneto-hydrodynamic simulation of an accreting, non-rotating black hole. For the first time, we are able to explain from first principles in…
The high energy emission of microquasars is thought to originate from high energy particles. Depending on the spectral state, the distribution of these particles can be thermal with a high temperature (typically 100 keV) or non-thermal and…
The spectral and timing properties of an oscillating hot thermal corona are investigated. This oscillation is assumed to be due to a magneto-acoustic wave propagating within the corona and triggered by an external, non specified,…
We investigate the accretion process in high-luminosity AGNs (HLAGNs) in the scenario of the disk evaporation model. Based on this model, the thin disk can extend down to the innermost stable circular orbit (ISCO) at accretion rates higher…
We have used observations of Cygnus X-1 from the Compton Gamma-Ray Observatory (CGRO) and BeppoSAX to study the variation in the MeV gamma-ray emission between the hard and soft spectral states, using spectra that cover the energy range 20…
We studied the polarization properties of Cygnus X-1 in both hard and soft spectral states with Imaging X-ray Polarimetry Explorer (IXPE) observations. The polarization degree is $\sim4$%, and $\sim 2.6-2.8$% in the hard and soft states,…
We report the results from our timing analysis of 15 RXTE observations of Cygnus X-1 throughout its 1996 spectral transitions. The entire period can be divided into 3 distinct phases: (1) transition from the hard to soft state, (2) soft…
(Abridged) We revisit the question of the nature of ULXs through a detailed investigation of their spectral shape, using the highest quality X-ray data available in the XMM-Newton public archives. We confirm that simple spectral models…
We report on the 0.5--200 keV spectral properties of Cyg X-1 observed at different epochs with the Narrow Field Instruments of the BeppoSAX satellite. The source was in its soft state during the first observation of 1996 June. In the second…
We investigate a corona coupled with underlying disk through magnetic field and radiation field, and present emergent spectra calculated from Monte Carlo simulations. The spectra are determined for given black-hole mass and accretion rate.…
The corona, a hot cloud of electrons close to the centre of the accretion disc, produces the hard X-ray power-law continuum commonly seen in luminous Active Galactic Nuclei (AGN). The continuum has a high-energy turnover, typically in the…
Cygnus X-1 was the first X-ray source widely accepted to be a black hole candidate and remains among the most studied astronomical objects in its class. The detection of non-thermal radio, hard X-rays and gamma rays reveals the fact that…
Hard X-ray spectra of black hole binaries in the low/hard state are well modeled by thermal Comptonization of soft seed photons by a corona-type region with $kT$\thinspace$\sim 50${\thinspace}keV and optical depth around 1. Previous…
Unified X-ray spectral and timing studies of Cygnus X-1 in the low/hard and hard intermediate state were conducted in a model-independent manner, using broadband Suzaku data acquired on 25 occasions from 2005 to 2009 with a total exposure…
We apply a model of magnetically dominated coronae above standard accretion discs to the low/hard state of galactic black holes. When the disc-corona coupling is accounted for self-consistently assuming that magneto-rotational instability…
The geometry of the accretion flow around stellar mass and supermassive black holes depends on the accretion rate. Broad iron emission lines originating from the irradiation of cool matter can indicate that there is an inner disk below a…