A Reflection Model with a Radial Disk Density Profile

Askar B Abdikamalov,Honghui Liu,Ashutosh Tripathi,Dimitry Ayzenberg,Cosimo Bambi

doi:10.3847/1538-4357/ac3237

Abstract

Abstract 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 ionization parameter also has a nonconstant radial profile and is calculated self-consistently from the electron density and the emissivity. We show the impact of the implementation of the electron density gradient in our model by analyzing a NuSTAR spectrum of the Galactic black hole in EXO 1846–031 during its last outburst in 2019 and a putative future observation of the same source with Athena and eXTP. For the NuSTAR spectrum, we find that the new model provides a better fit, but there is no significant difference in the estimation of the model parameters. For the Athena+eXTP simulation, we find that a model without a disk density profile is unsuitable to test the spacetime metric around the compact object in the sense that modeling uncertainties can incorrectly lead to finding a nonvanishing deformation from the Kerr solution.

Highlights

Blurred reflection features observed in the X-ray spectra of Galactic black holes and active galactic nuclei are thought to be produced by illumination of a cold accretion disk by a hot corona (Fabian et al 1989; Reynolds & Nowak 2003; Risaliti et al 2013; Bambi et al 2021)
We have presented relxilldgrad nk, which is an extension of the relxill nk package in which the disk electron density profile is described by a power-law and the ionization parameter is calculated self-consistently from the electron density and the emissivity
In order to see the impact of this implementation on the fits of reflection dominated spectra, in the previous section we have used relxill nk, relxillion nk, and relxilldgrad nk to fit a NuSTAR observation of EXO 1846–031 and the simulated simultaneous observation Athena+eXTP of the same source

Summary

INTRODUCTION

Blurred reflection features observed in the X-ray spectra of Galactic black holes and active galactic nuclei are thought to be produced by illumination of a cold accretion disk by a hot corona (Fabian et al 1989; Reynolds & Nowak 2003; Risaliti et al 2013; Bambi et al 2021). There are four main relativistic reflection models used by the X-ray astronomy community: kyn (Dovciak et al 2004), reflkerr (Niedzwiecki & Zycki 2008; Niedzwiecki et al 2019), relxill (Dauser et al 2013; Garcıa et al 2014), and the more recent reltrans (Ingram et al 2019) All these models employ, even if at different levels, the xillver model (Garcıa & Kallman 2010; Garcıa et al 2013) for the calculation of the reflection spectrum in the rest-frame of the gas in the disk and are today the most accurate models used in the analysis of relativistic reflection features.

RADIAL DISK DENSITY PROFILE

NuSTAR spectrum of EXO 1846–031

Simulation with Athena and eXTP

Findings

DISCUSSION AND CONCLUSIONS