Broadband Spectral properties of MAXI J1348--630 using AstroSat Observations

TL;DR

This study analyzes broadband X-ray spectra of the black hole binary MAXI J1348--630 using AstroSat, revealing details about its spectral states, black hole spin, and accretion disc properties.

Contribution

First broadband spectral analysis of MAXI J1348--630 with AstroSat, constraining black hole spin and disc inclination across different spectral states.

Findings

Black hole spin parameter a_* > 0.97

Disc inclination angle i ≈ 33 degrees

Inner disc radius not significantly truncated in hard states

Abstract

We present broadband X-ray spectral analysis of the black hole X-ray binary MAXI J1348--630, performed using five AstroSat observations. The source was in the soft spectral state for the first three and in the hard state for the last two observations. The three soft state spectra were modelled using a relativistic thin accretion disc with reflection features and thermal Comptonization. Joint fitting of the soft state spectra constrained the spin parameter of the black hole $a_*$ $>$ 0.97 and the disc inclination angle $i$ = 32.9$\substack{+4.1 \\ -0.6}$ degrees. The bright and faint hard states had bolometric flux a factor of $\sim 6$ and $\sim 10$ less than that of the soft state. Their spectra were fitted using the same model except that the inner disc radius was not assumed to be at the last stable orbit. However, the estimated values do not indicate large truncation radii and the inferred accretion rate in the disc was an order of magnitude lower than that of the soft state. Along with earlier reported temporal analysis, AstroSat data provides a comprehensive picture of the evolution of the source.