Testing Regular Black Holes with X-ray data of GX 339-4

TL;DR

This study tests regular black hole models by analyzing high-quality X-ray data from GX 339-4, providing the most stringent observational constraints on the regularization parameter to date.

Contribution

It extends previous work by applying simultaneous NuSTAR and Swift observations to constrain the regularization parameter in regular black hole models using X-ray spectral data.

Findings

Constraint on regularization parameter l/M < 0.44 at 90% CL

Stronger observational bounds than previous X-ray and gravitational wave studies

Successful analysis of thermal and reflection spectra for testing black hole models

Abstract

Regular black holes are singularity-free black hole spacetimes proposed to solve the problem of the presence of spacetime singularities that plagues the black holes of general relativity and most theories of gravity. In this work, we consider the regular black holes recently proposed by Mazza, Franzin & Liberati and we extend previous studies to get a more stringent observational constraint on the regularization parameter $l$. We study simultaneous observations of NuSTAR and Swift of the Galactic black hole in GX 339-4 during its outburst in 2015. The quality of the NuSTAR data is exceptionally good and the spectrum of the source presents both a strong thermal component and prominent relativistically blurred reflection features. This permits us to measure the regularization parameter $l$ from the simultaneous analysis of the thermal spectrum and the reflection features. From our analysis, we find the constraint $l/M < 0.44$ (90% CL), which is stronger than previous constraints inferred with X-ray and gravitational wave data.