Toward 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 that 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 α ₁₃ and α ₂₂, which quantify deviations from the Kerr metric. For α ₂₂ = 0, we obtain the black hole spin 0.928< {a}_* < 0.983 and -0.44< {α }₁₃< 0.15. For α ₁₃ = 0, we obtain 0.885< {a}_* < 0.987 and -0.12< {α }₂₂< 1.05. The Kerr solution is recovered for α ₁₃ = α 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.