Can the observation of ``shadow'' allow us to distinguish a black hole from more exotic compact object? We study motion photons in class vacuum static axially symmetric space-times that is continuously linked Schwarzschild metric through value one parameter can be interpreted as measure deformation source. investigate lensing effect and shadow produced by source with aim comparing expected image hole. In context astrophysical holes, we found it may not possible an small However, increases,...

Abstract Astrophysical black hole systems are the ideal laboratories for testing Einstein’s theory of gravity in strong field regime. We have recently developed a framework that uses reflection spectrum to perform precision tests general relativity by Kerr hypothesis. In this paper, we analyze XMM-Newton and NuSTAR observations supermassive Seyfert 1 galaxy MCG–06–30–15 with our disk model. consider Johannsen metric deformation parameters α 13 22 , which quantify deviations from metric. For...

Abstract X-ray reflection spectroscopy is a powerful tool for probing the strong gravity region of black holes and can be used testing general relativity in field regime. Simplifications available relativistic models limit capability performing accurate measurements properties holes. In this paper, we present an extension model relxill _ nk which accretion disk has finite thickness rather than being infinitesimally thin. We employ geometry proposed by Taylor & Reynolds construct...

Abstract Einstein’s theory of General Relativity predicts that the spacetime metric around astrophysical black holes is described by Kerr solution. In this work, we employ state-of-the-art relativistic reflection modeling to analyze a selected set NuSTAR spectra Galactic obtain most robust and precise constraints on hole hypothesis possible today. Our are much more stringent than those from other electromagnetic techniques and, with some sources, find stronger currently available gravitational waves.

Weyl conformal symmetry can solve the problem spacetime singularities present in Einstein's gravity. In a recent paper, two of us have found singularity-free rotating black hole solution addition to mass $M$ and spin angular momentum $J$ hole, new has parameter, $L$, which here we consider be proportional mass. Since is conformally equivalent Kerr metric, photon trajectories are unchanged, while structure an accretion disk around affected by value parameter $L$. this show that X-ray data...

We present the study of a sample seven "bare" active galactic nuclei (AGN) observed with Suzaku. interpret spectrum these sources relativistic reflection component and we employ our model RELXILL_NK to test Kerr nature their supermassive black holes. constrain Johannsen deformation parameters $\alpha_{13}$ $\alpha_{22}$, in which metric is recovered when $\alpha_{13} = \alpha_{22} 0$. All measurements are consistent hypothesis that spacetime geometry around objects described by solution. For...

Abstract In a previous paper, we tried to test the Kerr nature of stellar-mass black hole in GRS 1915+105 by analyzing NuSTAR data 2012 with our reflection model relxill _ nk . We found that choice intensity profile component is crucial and eventually were not able get any constraint on spacetime metric around 1915+105. present study same source Suzaku 2007. confirm plays an important role, but now find quite stringent constraints consistent hypothesis. The key differences respect are likely...

The continuum-fitting and the iron-line methods are currently two leading techniques for measuring spins of accreting black holes. In past few years, these have been developed testing fundamental physics. present work, we employ state-of-the-art models to test holes through analyze three NuSTAR observations hole binary GRS 1716-249 during its outburst in 2016-2017. observations, source was a hard-intermediate state spectra show both strong thermal component prominent relativistic reflection...

Abstract We present a new model to calculate reflection spectra of thin accretion disks in Kerr spacetimes. Our includes the effect returning radiation, which is radiation that emitted by disk and returns because strong light bending near black hole. The major improvement with respect existing models it calculates spectrum at every point on using actual incident radiation. Assuming lamppost coronal geometry, we simulate simultaneous observations NICER NuSTAR bright Galactic holes fit...

Abstract It is thought that the spacetime metric around astrophysical black holes well described by Kerr solution of Einstein’s gravity. However, robust observational evidence nature these objects still lacking. Here we fit X-ray spectrum stellar-mass hole in GS 1354–645 with a disk reflection model beyond gravity order test hypothesis. We consider Johannsen deformation parameters α 13 and 22 . The recovered for <?CDATA ${\alpha }_{13}={\alpha }_{22}=0$?> For = 0, our measurements spin...

Einstein's theory of general relativity has been extensively tested in weak gravitational fields, mainly with experiments the Solar System and observations radio pulsars, current data agree well theoretical predictions. Nevertheless, there are a number scenarios beyond gravity that have same predictions for fields present deviations only when becomes strong. Here, we try to test strong field regime. We fit x-ray spectrum supermassive black hole Ark 564 disk reflection model gravity, able...

Relativistic reflection features in the X-ray spectra of black hole binaries and AGNs are thought to be produced through illumination a cold accretion disk by hot corona. In this work, we assume that corona has shape an infinitesimally thin with its central axis same as rotational hole. The can either static or corotate disk. We calculate disk's emissivity profiles iron line shapes for set coronal radii heights. incorporate these into RELXILL_NK simulate some observations binary NuSTAR study...

The continuum-fitting and the iron line methods are currently two leading techniques for probing strong gravity region around accreting black holes. In present work, we test Kerr hole hypothesis with stellar-mass in GRS 1915+105 by analyzing five disk-dominated RXTE spectra one reflection-dominated Suzaku spectrum. combination of constraints from has potential to provide more stringent tests metric. Our constraint on Johannsen deformation parameter $\alpha_{13}$ is $-0.15 < \alpha_{13} 0.14$...

Abstract Regular black holes are singularity-free hole spacetimes proposed to solve the problem of presence spacetime singularities that plagues general relativity and most theories gravity. In this work, we consider regular recently by Mazza, Franzin &amp; Liberati extend previous studies get a more stringent observational constraint on regularization parameter l . We study simultaneous observations NuSTAR Swift Galactic in GX 339–4 during its outburst 2015. The quality data is...

We present the public release version of relxill_nk, an X-ray reflection model for testing Kerr hypothesis and general relativity. This extends relxill that assumes black hole spacetime is described by metric. also relxilllp_nk, first non-Kerr with a lamppost corona configuration, as well all other models available in full relxill_nk package. In relevant relativistic effects are calculated through ray-tracing code can be applied to any well-behaved, stationary, axisymmetric, asymptotically...

The iron line and the continuum-fitting methods are currently two leading techniques for measuring black hole spins with electromagnetic radiation. They can be naturally extended probing spacetime geometry around holes testing general relativity in strong field regime. In past couple of years, there has been significant work to use method test nature holes. this Letter, we show its capability constraining by analyzing 17 RXTE data X-ray binary LMC X-1.

Very steep reflection emissivity profiles in the inner part of accretion disks are commonly found analysis x-ray observations black hole binaries and active galactic nuclei, but there is some debate about their exact origin. While can be naturally produced by compact coronae close to holes, measured radial parameter further increased disk ionization profile when theoretical model assumes a with constant ionization. In this paper, we implement possibility relxill_nk, which package designed...

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 to General Relativity. Recently, some authors have explored its astrophysical implications in spectra accreting black holes inferred constraint $r_2 < 0.1$, where \ge 0$ hole dilaton charge Relativity recovered for = 0$. In present paper, we study impact non-vanishing on reflection spectrum disk. From analysis...

Abstract In the disk–corona model, X-ray spectrum of a stellar-mass black hole in an binary is characterized by three components: thermal component from thin and cold accretion disk, Comptonized hot corona, reflection produced illumination disk corona. this paper, we assume lamppost improve previous calculations binaries. The direct radiation corona as well returning components calculated considering actual illuminating disk. If turn off, completely generated component, it may happen for...

We continue exploring the constraining capabilities of x-ray reflection spectroscopy to test Kerr-nature astrophysical black holes, and we present results our analysis two NuSTAR observations Cygnus X-1 in soft state. find that final measurement can strongly depend on assumption intensity profile. conclude is not suitable for tests general relativity using spectroscopy, discuss desired properties a source be good candidate studies.

We present nkbb, an XSPEC model for the thermal spectrum of thin accretion disks in parametric black hole spacetimes. employ Novikov-Thorne description disk and formalism transfer function proposed by Cunningham storing all relativistic effects spacetime metric. The current version assumes Johannsen metric, but it can be easily extended to any stationary, axisymmetric, asymptotically flat without pathological properties. used within package test Kerr nature astrophysical holes with...

Kaluza-Klein theory is a popular alternative of gravity, with both non-rotating and rotating black hole solutions known. This allows for the possibility that could be observationally tested. We present model which calculates reflection spectrum accretion disk system, where described by solution theory. also use this to analyze X-ray data from stella-mass in GRS 1915+105 provide constraints on free parameters holes.

X-ray reflection spectroscopy is a promising technique for testing general relativity in the strong field regime, as it can be used to test Kerr black hole hypothesis. In this context, parametrically deformed metrics proposed by Konoplya, Rezzolla \& Zhidenko (Phys. Rev. D93, 064015, 2016) form an important class of non-Kerr holes. We implement \textsc{relxill\_nk}, which framework we have developed holes using spectroscopy. perform qualitative analysis effect leading order strong-field...

Asymptotically safe quantum gravity is a promising candidate scenario to provide UV extension for the effective field theory of Einstein's gravity. The has its foundations on very successful framework theory, which been extensively tested electromagnetic and nuclear interactions. However, observational tests asymptotically are more challenging. Recently, rotating black hole metric inspired by proposed, this opens possibility astrophysical theory. In present paper, we show capabilities X-ray...

Abstract The presence of spacetime singularities in physically relevant solutions the Einstein Equations is normally interpreted as a symptom breakdown classical general relativity at very high densities/curvatures. However, despite significant efforts past decades, we do not have yet any robust theoretical framework to solve problem singularities. In this context, few years seen an increasing interest study phenomenological scenarios describe singularity-free black holes, gravitational...