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

TL;DR

This study uses X-ray reflection spectroscopy to test deviations from the Kerr black hole model around supermassive black holes, finding results consistent with Kerr but with some parameters poorly constrained.

Contribution

It extends the reflection spectroscopy framework to a broad class of non-Kerr black holes and applies it to real observational data.

Findings

Kerr solution is recovered in all cases

Some deviation parameters are poorly constrained

Results support Kerr black holes but highlight observational limitations

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.