# Broadband reflection spectroscopy of MAXI J1535-571 using AstroSat: Estimation of black hole mass and spin

## TL;DR

This study uses broadband AstroSat X-ray observations to analyze the black hole MAXI J1535-571, accurately estimating its spin, mass, and distance by modeling reflection spectra and emphasizing the importance of broadband analysis.

## Contribution

First broadband spectral analysis of MAXI J1535-571 during its outburst, constraining black hole spin, mass, and distance using advanced reflection models.

## Key findings

- Black hole spin estimated as 0.67^{+0.16}_{-0.04}
- Black hole mass estimated as 10.39^{+0.61}_{-0.62} M_{\u00b0}
- Distance estimated as 5.4^{+1.8}_{-1.1} kpc

## Abstract

We report the results from \textit{AstroSat} observations of the transient Galactic black hole X-ray binary MAXI J1535-571 during its hard-intermediate state of the 2017 outburst. We systematically study the individual and joint spectra from two simultaneously observing \textit{AstroSat} X-ray instruments, and probe and measure a number of parameter values of accretion disc, corona and reflection from the disc in the system using models with generally increasing complexities. Using our broadband ($1.3-70$ keV) X-ray spectrum, we clearly show that a soft X-ray instrument, which works below $\sim 10-12$ keV, alone cannot correctly characterize the Comptonizing component from the corona, thus highlighting the importance of broadband spectral analysis. By fitting the reflection spectrum with the latest version of the \textsc{relxill} family of relativistic reflection models, we constrain the black hole's dimensionless spin parameter to be $0.67^{+0.16}_{-0.04}$. We also jointly use the reflection spectral component (\textsc{relxill}) and a general relativistic thin disc component (\texttt{Kerrbb}), and estimate the black hole's mass and distance to be $10.39_{-0.62}^{+0.61} M_{\odot}$ and $5.4_{-1.1}^{+1.8}$ kpc respectively.