Reflection spectra of thick accretion discs

Abstract

Relativistic reflection features are commonly observed in the X-ray spectra of stellarmass and supermassive black holes and originate from illumination of the inner part of the accretion disk by a hot corona. All the available relativistic reflection models assume that the disk is infinitesimally thin and the inner edge is at the innermost stable circular orbit or at a larger radius. However, we know that several sources, especially among supermassive black holes, have quite high mass accretion rates. In such a case, the accretion disk becomes geometrically thick and the inner edge of the disk is expected to be inside the innermost stable circular orbit. In this work, we employ the Polish donut model to describe geometrically thick disks and we study the iron line shapes from similar systems. We also simulate full reflection spectra and we analyze the simulated observations with a thin disk relativistic reflection model to determine the impact of the disk structure on the estimation of the model parameters, in particular in the case of tests of the Kerr hypothesis.

Testing Evolution of LFQPOs with Mass Accretion Rate in GRS 1915+105 with Insight-HXMT

“…Once the origin of the QPOs is understood, the behavior of the QPOs can help to reveal the spacetime properties in the vicinity of the black hole (e.g., Motta et al 2014). We have been able to test the Kerr hypothesis using the reflection-dominated (Zhang et al 2019b) and thermaldominated (Tripathi et al 2020) X-ray spectra of black hole XRBs, although systematic uncertainties in modeling can somehow affect the analysis (e.g., Liu et al 2019;Zhang et al 2019a;Riaz et al 2020). In the particularly interesting source GRS 1915+105, we can apply the continuum fitting method, reflection spectroscopy, and QPO modeling together to constrain a possible deviation from the Kerr metric.…”

Testing general relativity with x-ray reflection spectroscopy: The Konoplya-Rezzolla-Zhidenko parametrization

“…The Kerr solution lies at δ i ¼ 0 in each plot. assumption can potentially cause systematic error in spin up to 0.2 [86] and 0.4 [87], and more than 1 for deformation parameters [61]. Another assumption, that particles move in circular orbits on the disk can also lead to systematic errors [88].…”

“…The inset shows conversion of incident radiation in to reflected radiation. Studies of their effect on the reflection spectrum in the presence of non-Kerr metrics is an ongoing effort[61,62].More details can be found on the public version webpage at Refs. [63,64].…”

Testing the Kerr Black Hole Hypothesis Using X-Ray Reflection Spectroscopy and a Thin Disk Model with Finite Thickness

“…All the available relativistic reflection models assume that the black hole accretion disk is geometrically thin and that there is no emission of radiation inside the inner edge of the disk. For example, if we apply these models to sources accreting near their Eddington limit, the spin parameter can be easily overestimated (Riaz et al 2019(Riaz et al , 2020. Moreover, the accretion disk is always approximated as infinitesimally thin.…”