Towards precision tests of general relativity with black hole X-ray reflection spectroscopy

Abstract

Astrophysical black hole systems are the ideal laboratories for testing Einstein's theory of gravity in the strong field regime. We have recently developed a framework which uses the reflection spectrum of black hole systems to perform precision tests of general relativity by testing the Kerr black hole hypothesis. In this paper, we analyze XMM-Newton and NuSTAR observations of the supermassive black hole in the Seyfert 1 galaxy MCG-06-30-15 with our disk reflection model. We consider the Johannsen metric with the deformation parameters ${\alpha }_{13}$ and ${\alpha }_{22}$, which quantify deviations from the Kerr metric. For ${\alpha }_{22}=0$, we obtain the black hole spin $0.928<a_{\ast }<0.983$ and $-0.44<{\alpha }_{13}<0.15$. For ${\alpha }_{13}=0$, we obtain $0.885<a_{\ast }<0.987$ and $-0.12<{\alpha }_{22}<1.05$. The Kerr solution is recovered for ${\alpha }_{13}={\alpha }_{22}=0$. Thus, our results include the Kerr solution within statistical uncertainties. Systematic uncertainties are difficult to account for, and we discuss some issues in this regard.

10 pages, 7 figures. v2: title slightly changed, arXiv version shorter than published version