Constraining the KRZ deformation parameters I: limits from supermassive black hole X-ray data

Abstract

X-ray reflection spectroscopy is a powerful technique for probing the nature of gravity around black holes in the so-called strong field regime. One of the most popular of such probes is to look at theory-agnostic deviations away from the Kerr solution, which is the only astrophysically relevant black hole solution within classical general relativity, in order to verify whether astrophysical black holes are described by the Kerr metric. We have recently extended our X-ray reflection spectroscopy framework to a class of very general axisymmetric non-Kerr black holes proposed by Konoplya, Rezzolla & Zhidenko (Phys. Rev. D93, 064015, 2016). Here, we analyze XMM-Newton and NuSTAR observations of the supermassive black hole in the Seyfert 1 galaxy MCG-06-30-15 with six different deviation parameters of this extended model. We recover the Kerr solution in all cases, but some deformation parameters are poorly constrained. We discuss the implications of this verification and future possibilities.

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

“…In the present work, we have extended that study to constrain the KRZ deformation parameters with a stellar-mass BH. The constraints from stellar-mass and supermassive BHs can indeed test different physics because they probe different curvature regimes [27]. In some theories, new physics may be more easily discovered from the study of lighter BHs and in other models we may have the opposite case with larger deviations from the Kerr solution in heavier BHs.…”

“…More details can be found in Refs. [25][26][27]32]. The KRZ metric uses a continued-fraction-based parametrization of stationary and axisymmetric spacetimes, with asymptotic flatness imposed a posteriori.…”

“…[26] (wherein we also analyze the effect of the deformation parameters on the reflection spectrum and present the implementation of the KRZ metric in the data analysis framework) and MCG-06-30-15 in Ref. [27] (hereafter Paper I). Here we instead study a stellar-mass BH, and we can thus probe a different curvature regime.…”