Related papers: Constraining Black Hole Spin Via X-ray Spectroscop…
In most accreting black-hole systems the copious X-rays commonly observed from the inner-most regions are accompanied by a reflection spectrum. The latter is the signature of energetic photons reprocessed by the optically thick material of…
X-ray reflection features observed from the innermost regions of accretion disks in Active Galactic Nuclei (AGNs) allow important tests of accretion theory. In recent years it has been possible to use the Fe K line and reflection continuum…
Spin parameters of stellar-mass black holes in X-ray binaries are currently being estimated by fitting the X-ray continuum spectra of their accretion disk emission. For this method, it is necessary to know the inclination of the…
We present an analysis of XMM-Newton observations of eleven Seyfert galaxies that appear to be missing a broad iron K alpha line. These objects represent a challenge to the established paradigm for active galactic nuclei, where a relatively…
We review current challenges in understanding the values and origin of the spins of black holes in binaries. Thanks to recent advances in astrophysical instrumentation, the spins can now be measured using both gravitational waves emitted by…
Astrophysical black holes are thought to be the Kerr black holes predicted by general relativity, but macroscopic deviations from the Kerr solution can be expected from a number of scenarios involving new physics. In Paper I, we studied the…
We discuss a model of an X-ray illuminating source above an accretion disk of a rotating black hole. Within the so called lamp-post scheme we compute the expected (observed) polarization properties of the radiation reaching an observer. We…
Signatures of X-ray reprocessing (reflection) out of an accretion disk are commonly observed in the high-energy spectrum of accreting black holes, and can be used to probe the strong gravity region around these objects. In this paper, we…
We study the persistent black hole X-ray binary Cyg X-1, recently observed by XRISM Resolve and simultaneously by NICER and NuSTAR in its hard spectral state. We confirm the result of Draghis et al.\ that fits of the Resolve data alone with…
The relativistically broadened iron K-alpha line at 6.4 keV observed in the Seyfert 1 galaxy MCG-6-30-15 has provided a probe of the strong-gravity environment near a black hole, in particular suggesting that it is rapidly spinning. An…
We present an analysis of the X-ray spectra of a sample of 37 observations of 26 Seyfert galaxies observed by XMM-Newton in order to characterize their iron K emission. All objects show evidence for iron line emission in the 6-7 keV band. A…
We use the method of Press, Rybicki & Hewitt (1992) to search for time lags and time leads between different energy bands of the RXTE data for MCG-6-30-15. We tailor our search in order to probe any reverberation signatures of the…
Fairall 9 is one of several type 1 active galactic nuclei for which it has been claimed that the angular momentum (or spin) of the supermassive black hole can be robustly measured, using the Fe K$\alpha$ emission line and Compton-reflection…
4U 1543-47 is a low mass X-ray binary which harbours a stellar-mass black hole located in our Milky Way galaxy. In this paper, we revisit 7 data sets which were in the Steep Power Law state of the 2002 outburst. The spectra were observed by…
In active galactic nuclei, X-ray illumination of the accretion disk around a supermassive black hole (SMBH) results in the production of the K$\alpha$ fluorescent line of iron, which provides insights into accretion physics and SMBH spins.…
We present an analysis of the 2-10keV XMM-Newton/EPIC-pn spectrum of the Seyfert-1 galaxy NGC4593. Apart from the presence of two narrow emission lines corresponding to the Kalpha lines of cold and hydrogen-like iron, this spectrum…
The black-hole spin parameter, $a_*$, was measured to be close to its maximum value of 1 in many accreting X-ray binaries. In particular, $a_*\gtrsim 0.9$ was found in a number of studies of LMC X-1. These measurements were claimed to take…
In a recent paper [Ghasemi-Nodehi & Bambi, EPJC 76 (2016) 290], we have proposed a new parametrization for testing the Kerr nature of astrophysical black hole candidates. In the present work, we study the possibility of constraining the…
Detecting and modelling the reprocessed hard X-ray emission component in the accretion flow, so-called reflection spectrum is a main tool to estimate black hole spins in a wide range of astrophysical black holes regardless of their mass or…
A model for the inner regions of accretion flows is presented where, due to disc instabilities, cold and dense material is clumped into deep sheets or rings. Surrounding these density enhancements is hot, tenuous gas where coronal…