Suzaku Observation of the Black Hole Candidate MAXI J1836-194 in a Hard/Intermediate Spectral State

TL;DR

This study uses Suzaku X-ray observations to analyze MAXI J1836-194, revealing a relativistically broadened iron line indicative of a rapidly spinning stellar-mass black hole in a hard/intermediate spectral state.

Contribution

First detailed spectral analysis of MAXI J1836-194 confirming a high black hole spin using reflection modeling in a hard/intermediate state.

Findings

Black hole spin estimated at 0.88±0.03

Relativistically broadened iron line detected

Consistent results across different spectral models

Abstract

We report on a Suzaku observation of the newly discovered X-ray binary MAXI J1836-194. The source is found to be in the hard/intermediate spectral state and displays a clear and strong relativistically broadened iron emission line. We fit the spectra with a variety of phenomenological, as well as physically motivated disk reflection models, and find that the breadth and strength of the iron line is always characteristic of emission within a few gravitational radii around a black hole. This result is independent of the continuum used and strongly points toward the central object in MAXI J1836-194 being a stellar mass black hole rotating with a spin of $a=0.88\pm0.03$ (90% confidence). We discuss this result in the context of spectral state definitions, physical changes (or lack thereof) in the accretion disk and on the potential importance of the accretion disk corona in state transitions.