Constraining the Konoplya-Rezzolla-Zhidenko deformation parameters II: limits from stellar-mass black hole X-ray data

TL;DR

This study uses X-ray data from a stellar-mass black hole to test deviations from the Kerr black hole model, finding results consistent with general relativity but with some parameters remaining unconstrained.

Contribution

It extends previous work by analyzing stellar-mass black hole data to constrain deformation parameters, exploring a different curvature regime.

Findings

Results are consistent with Kerr black holes.

Some deformation parameters remain unconstrained.

No significant deviations from general relativity detected.

Abstract

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 scenarios involving new physics. In Paper I, we studied the reflection features in NuSTAR and XMM-Newton spectra of the supermassive black hole at the center of the galaxy MCG-06-30-15 and we constrained a set of deformation parameters proposed by Konoplya, Rezzolla & Zhidenko (Phys. Rev. D93, 064015, 2016). In the present work, we analyze the X-ray data of a stellar-mass black hole within the same theoretical framework in order to probe a different curvature regime. We consider a NuSTAR observation of the X-ray binary EXO 1846-031 during its outburst in 2019. As in the case of Paper I, all our fits are consistent with the Kerr black hole hypothesis, but some deformation parameters cannot be constrained well.