relxill_nk: A Relativistic Reflection Model for Testing Einstein’s Gravity

Abstract

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.

About the Kerr Nature of the Stellar-mass Black Hole in GRS 1915+105

“…X-ray reflection spectroscopy is potentially a powerful technique to test the Kerr nature of astrophysical black holes with electromagnetic radiation [12][13][14][15][16][17][18][19]. This * Corresponding author: bambi@fudan.edu.cn technique is based on the study of the reflection spectrum of accretion disks [20,21].…”

Testing General Relativity with Supermassive Black Holes Using X-Ray Reflection Spectroscopy

“…In the past one and a half years, we have analyzed X-ray observations of 4 stellar-mass black holes [46][47][48][49] and 11 supermassive black holes [45,[50][51][52][53][54][55] with relxill nk. Supermassive black holes are probably more suitable than the stellar-mass ones for our tests, because their spectrum is easier to model (as the temperature of the accretion disk is lower) and they typically rotate very fast (so the inner edge of the accretion disk is closer to the black hole event horizon and the radiation emitted from the inner part of the accretion disk is more strongly affected by relativistic effects).…”

Singularity-free black holes in conformal gravity: New observational constraints

“…The model employs the Johannsen metric [41] and has been used to test the Kerr metric with the supermassive black holes in 1H0707-495 [19] and Ark 564 [20], and the stellar mass black hole in GX 339-4 [21] (for a summary of current constraints, see Ref. [22]). In the present paper, we will use a modified version of relxill nk employing the black hole metric in Eq.…”

“…In Ref. [17], we employed a modified version of the reflection model relxill nk [18][19][20][21][22], and we analyzed the 2014 observations of NuSTAR and Swift of the supermassive black holes in 1H0707-495, obtaining the constraint L/M < 0.45 (90% confidence level). However, 1H0707-495 is quite a controversial source, not fully understood at the moment, and therefore the constraint is not robust.…”