Impact of the disk thickness on X-ray reflection spectroscopy measurements

TL;DR

This study extends X-ray reflection models to include finite disk thickness and applies it to real data, confirming that disk thickness has minimal impact on black hole spin measurements in high accretion systems.

Contribution

The paper introduces a reflection model extension accounting for finite disk thickness and demonstrates its robustness in spin measurements using observational data.

Findings

Disk thickness does not significantly alter spin measurements in high radiative efficiency disks.

The model confirms previous spin results obtained with thin disk assumptions.

Future work will test the impact on lower accretion rate systems.

Abstract

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 & Reynolds (2018). In this paper, we apply our model to fit the 2013 simultaneous observations by NuSTAR and XMM-Newton of the supermassive black hole in MCG-06-30-15 and the 2019 NuSTAR observation of the Galactic black hole in EXO 1846-031. The high-quality data of these spectra had previously led to precise black hole spin measurements and very stringent constraints on possible deviations from the Kerr metric. We find that the disk thickness does not change previous spin results found with a model employing an infinitesimally thin disk, which confirms the robustness of spin measurements in high radiative efficiency disks, where the impact of disk thickness is minimal. Similar analysis on lower accretion rate systems will be an important test for measuring the effect of disk thickness on black hole spin measurements.