145 citations · 1.3k across the 55 of their papers we have counts for
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Measuring black hole spins with x-ray reflection spectroscopy: A GRMHD outlook
Swarnim Shashank, Askar B. Abdikamalov, Honghui Liu +4
X-ray reflection spectroscopy has evolved as one of the leading methods to measure black hole spins. However, the question is whether its measurements are subjected to systematic b…
About the accuracy of the relxill/relxill_nk models in view of the next generation of X-ray missions
Honghui Liu, Askar B. Abdikamalov, Temurbek Mirzaev +4
X-ray reflection spectroscopy is a powerful tool to study the strong gravity region of black holes. The next generation of astrophysical X-ray missions promises to provide unpreced…
Modeling reflection spectra of super-Eddington X-ray sources
Swarnim Shashank, Askar B. Abdikamalov, Honghui Liu +5
Relativistic reflection is a common feature in the X-ray observations of accreting compact objects. We present reflux, a new X-ray reflection model for spectral analysis of super-E…
X-ray spectra of black hole X-ray binaries with returning radiation
Temurbek Mirzaev, Cosimo Bambi, Askar B. Abdikamalov +4
In the disk-corona model, the X-ray spectrum of a stellar-mass black hole in an X-ray binary is characterized by three components: a thermal component from a thin and cold accretio…
Testing General Relativity with NuSTAR data of Galactic Black Holes : II
Ashutosh Tripathi, Swarnim Shashank, Gitika Mall +1
General relativity predicts the spacetime metric around an astrophysical black hole to be described by the Kerr solution, which is a massive rotating black hole without any residua…
Towards more accurate synthetic reflection spectra: improving the calculations of returning radiation
Temurbek Mirzaev, Shafqat Riaz, Askar B. Abdikamalov +6
We present a new model to calculate reflection spectra of thin accretion disks in Kerr spacetimes. Our model includes the effect of returning radiation, which is the radiation that…
Testing Regular Black Holes with X-ray data of GX 339-4
Shafqat Riaz, Michail Kyriazis, Askar B. Abdikamalov +2
Regular black holes are singularity-free black hole spacetimes proposed to solve the problem of the presence of spacetime singularities that plagues the black holes of general rela…
Impact of the returning radiation in current tests of the Kerr black hole hypothesis using X-ray reflection spectroscopy
Shafqat Riaz, Temurbek Mirzaev, Askar B. Abdikamalov +1
The past 10 years have seen remarkable progress in our capability of analyzing reflection features in the X-ray spectra of accreting black holes. Today X-ray reflection spectroscop…
Testing relativistic reflection models with GRMHD simulations of accreting black holes
Swarnim Shashank, Shafqat Riaz, Askar B. Abdikamalov +1
X-ray reflection spectroscopy is currently one of the leading techniques for studying the inner part of accretion disks around black holes, measuring black hole spins, and even tes…
Impact of ionization and electron density gradients in X-ray reflection spectroscopy measurements
Gitika Mall, Ashutosh Tripathi, Askar B. Abdikamalov +1
The models currently used for the analysis of the reflection spectra of black holes usually assume a disk with constant ionization and electron density. However, there is some deba…
Black Hole Spin Measurements Based on a Thin Disc Model with Finite Thickness I. An example study of MCG-06-30-15
Jiachen Jiang, Askar B. Abdikamalov, Cosimo Bambi +1
We present a re-analysis of the XMM-Newton and NuSTAR observing campaign for the well-studied, X-ray-bright AGN MCG-06-30-15. In particular, we consider a disc model with finite th…
A reflection model with a radial disk density profile
Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi +2
In this paper we present RELXILLDGRAD_NK, a relativistic reflection model in which the electron density of the accretion disk is allowed to have a radial power-law profile. The ion…
Constraining the Konoplya-Rezzolla-Zhidenko deformation parameters II: limits from stellar-mass black hole X-ray data
Zhibo Yu, Qunfeng Jiang, Askar B. Abdikamalov +5
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…
Testing the Kerr black hole hypothesis with the continuum-fitting and the iron line methods: the case of GRS 1915+105
Ashutosh Tripathi, Askar B. Abdikamalov, Dimitry Ayzenberg +4
The continuum-fitting and the iron line methods are currently the two leading techniques for probing the strong gravity region around accreting black holes. In the present work, we…
Testing the Kerr black hole hypothesis with GRS 1716-249 by combining the continuum-fitting and the iron-line methods
Zuobin Zhang, Honghui Liu, Askar B. Abdikamalov +3
The continuum-fitting and the iron-line methods are currently the two leading techniques for measuring the spins of accreting black holes. In the past few years, these two methods…
Constraining the KRZ deformation parameters I: limits from supermassive black hole X-ray data
Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi +2
X-ray reflection spectroscopy is a powerful technique for probing the nature of gravity around black holes in the so-called strong field regime. One of the most popular of such pro…
Testing the Weak Equivalence Principle near black holes
Rittick Roy, Askar B. Abdikamalov, Dimitry Ayzenberg +3
Today we have quite stringent constraints on possible violations of the Weak Equivalence Principle from the comparison of the acceleration of test-bodies of different composition i…
Constraints on Einstein-Maxwell dilaton-axion gravity from X-ray reflection spectroscopy
Ashutosh Tripathi, Biao Zhou, Askar B. Abdikamalov +2
Einstein-Maxwell dilaton-axion gravity is a string-inspired model arising from the low energy effective action of heterotic string theory and an important candidate as alternative…
Impact of the disk thickness on X-ray reflection spectroscopy measurements
Ashutosh Tripathi, Askar B. Abdikamalov, Dimitry Ayzenberg +2
In a previous paper, we presented an extension of our reflection model RELXILL_NK to include the finite thickness of the accretion disk following the prescription in Taylor & Reyno…
Probing the near-horizon region of Cygnus X-1 with Suzaku and NuSTAR
Zuobin Zhang, Honghui Liu, Askar B. Abdikamalov +3
Astrophysical black holes are ideal laboratories for testing Einstein's theory of general relativity in the strong field regime. In this manuscript, we present an analysis of Suzak…
Implementation of a radial disk ionization profile in the RELXILL_NK model
Askar B. Abdikamalov, Dimitry Ayzenberg, Cosimo Bambi +2
Very steep reflection emissivity profiles in the inner part of accretion disks are commonly found in the analysis of X-ray observations of black hole binaries and AGN, but there is…
Testing General Relativity with NuSTAR data of Galactic Black Holes
Ashutosh Tripathi, Yuexin Zhang, Askar B. Abdikamalov +5
Einstein's theory of General Relativity predicts that the spacetime metric around astrophysical black holes is described by the Kerr solution. In this work, we employ state-of-the-…
Reflection spectra of accretion disks illuminated by disk-like coronae
Shafqat Riaz, Askar B. Abdikamalov, Dimitry Ayzenberg +3
Relativistic reflection features in the X-ray spectra of black hole binaries and AGNs are thought to be produced through illumination of a cold accretion disk by a hot corona. In t…
Testing the Kerr Black Hole Hypothesis with GX 339-4 by a combined analysis of its thermal spectrum and reflection features
Ashutosh Tripathi, Askar B. Abdikamalov, Dimitry Ayzenberg +3
We analyze simultaneous observations with NuSTAR and Swift of the black hole binary GX 339-4 in which we clearly detect both a strong thermal component and prominent relativistic r…