An Extreme Black Hole in the Recurrent X-ray Transient XTE J2012+381

TL;DR

This study analyzes X-ray observations of the transient black hole XTE J2012+381 during its 2022 outburst, measuring a high spin parameter and examining spectral features to understand black hole properties and disk phenomena.

Contribution

It provides the first detailed relativistic reflection modeling of XTE J2012+381, measuring its black hole spin and inclination, and assesses the presence of disk winds with extensive spectral analysis.

Findings

Black hole spin measured as a=0.988^{+0.008}_{-0.030}

No statistically significant absorption lines detected

Relativistic reflection features consistent across models

Abstract

The black hole candidate XTE J2012+381 underwent an outburst at the end of 2022. We analyzed 105 NICER observations and 2 NuSTAR observations of the source during the outburst. The NuSTAR observations of the $M \sim10M_\odot$ black hole indicate clear signs of relativistic disk reflection, which we modeled to measure a BH spin of $a=0.988^{+0.008}_{-0.030}$ and an inclination of $\theta=68^{+6}_{-11}$ degrees ($1\sigma$ statistical errors). In our analysis, we test an array of models and examine the effect of fitting NuSTAR spectra alone versus fitting simultaneously with NICER. We find that when the underlying continuum emission is properly accounted for, the reflected emission is similarly characterized by multiple models. We combined 52 NICER spectra to obtain a spectrum with an effective exposure of 190 ks in order to probe the presence of absorption lines that would be suggestive of disk winds, but the resulting features were not statistically significant. We discuss the implications of this measurement in relation to the overall BH spin distribution in X-ray binary systems.