Broadband X-ray Spectroscopy and Estimation of Spin of the Galactic Black Hole Candidate GRS 1758-258

TL;DR

This study analyzes broadband X-ray spectra of the black hole candidate GRS 1758-258, revealing a high spin parameter (>0.92) and details about its accretion state and corona during a low hard state observation.

Contribution

It provides the first broadband spectral analysis of GRS 1758-258 using simultaneous Swift and NuSTAR data, estimating the black hole's spin and accretion properties.

Findings

Black hole spin > 0.92

In low hard state with corona temperature ~140 keV

Accretion rate approximately 1.5% of Eddington limit

Abstract

We present the results of a broadband (0.5-78 keV) X-ray spectral study of the persistent Galactic black hole X-ray binary GRS 1758-258 observed simultaneously by Swift and NuSTAR. Fitting with an absorbed power-law model revealed a broad Fe line and reflection hump in the spectrum. We used different flavours of the relativistic reflection model for the spectral analysis. All models indicate the spin of the black hole in GRS 1758-258 is >0.92. The source was in the low hard state during the observation, with the hot electron temperature of the corona estimated to be kT$_e$ ~ 140 keV. The black hole is found to be accreting at ~1.5 % of the Eddington limit during the observation, assuming the black hole mass of 10 $M_{\odot}$ and distance of 8 kpc.