RELXILL_NK: a relativistic reflection model for testing Einstein's gravity

TL;DR

RELXILL_NK is a novel relativistic reflection model designed to test Einstein's gravity near black holes by analyzing X-ray reflection spectra, providing new constraints on deviations from general relativity in strong gravitational fields.

Contribution

This paper introduces RELXILL_NK, the first model capable of probing spacetime metrics around black holes to test Einstein's gravity in the strong field regime.

Findings

Constraints on deviations from Einstein's gravity for multiple black holes.

First application of relativistic reflection modeling to test strong-field gravity.

Evidence supporting general relativity within current observational limits.

Abstract

Einstein's theory of general relativity was proposed over 100 years ago and has successfully passed a large number of observational tests in the weak field regime. However, the strong field regime is largely unexplored, and there are many modified and alternative theories that have the same predictions as Einstein's gravity for weak fields and present deviations when gravity becomes strong. RELXILL_NK is the first relativistic reflection model for probing the spacetime metric in the vicinity of astrophysical black holes and testing Einstein's gravity in the strong field regime. Here we present our current constraints on possible deviations from Einstein's gravity obtained from the black holes in 1H0707-495, Ark 564, GX 339-4, and GS 1354-645.