Testing the Kerr black hole hypothesis with the continuum-fitting and the iron line methods: the case of GRS 1915+105

TL;DR

This study tests the Kerr black hole hypothesis using continuum-fitting and iron line methods on GRS 1915+105, combining data from RXTE and Suzaku to constrain deviations from the Kerr metric.

Contribution

It demonstrates how combining two leading techniques can improve tests of the Kerr black hole hypothesis with stellar-mass black holes.

Findings

Constraint on Johannsen deformation parameter: -0.15 to 0.14 at 3σ

Combined spectral analysis enhances the test of Kerr metric

Supports Kerr black hole hypothesis within current observational limits

Abstract

The continuum-fitting and the iron line methods are currently the two leading techniques for probing the strong gravity region around accreting black holes. In the present work, we test the Kerr black hole hypothesis with the stellar-mass black hole in GRS 1915+105 by analyzing five disk-dominated RXTE spectra and one reflection-dominated Suzaku spectrum. The combination of the constraints from the continuum-fitting and the iron line methods has the potential to provide more stringent tests of the Kerr metric. Our constraint on the Johannsen deformation parameter $\alpha_{13}$ is $-0.15 < \alpha_{13} < 0.14$ at 3$\sigma$, where the Kerr metric is recovered when $\alpha_{13} = 0$.