Testing general relativity with X-ray reflection spectroscopy of MCG-06-30-15

TL;DR

This study uses X-ray reflection spectroscopy data from MCG-06-30-15 to test for deviations from the Kerr metric around black holes, constraining possible alternative gravity models.

Contribution

It introduces a modified RELXILL code to analyze real X-ray data for deviations from the Kerr solution in a generic black hole metric.

Findings

Constraints on the Johannsen deformation parameter $oldsymbol{eta_{13}}$

No significant deviations from Kerr detected

Provides bounds on alternative gravity theories

Abstract

The spacetime geometry around astrophysical black holes is well approximated by the Kerr metric, but deviations from standard predictions are possible in a number of scenarios beyond Einstein's gravity and in the presence of exotic matter. In this paper, we present the constraints on possible deviations from the Kerr solution using X-ray reflection spectroscopy from the analysis of real data. We use the relativistic X-ray reflection code RELXILL modified to a generic stationary, axisymmetric and asymptotically flat black hole metric. We analyze 350 ks long XMM-Newton observations of the AGN in MCG-06-30-15 taken during July-August 2001 and constrain the Johannsen deformation parameter $\alpha_{13}$.