Constraining Spin and Inclination Angle of XTE J2012+381 using AstroSat and NICER

TL;DR

This study uses combined NICER and AstroSat data to analyze the black hole X-ray binary XTE J2012+381, constraining its spin and inclination angle despite uncertainties in mass and distance, and finds a high-spin regime with well-constrained inclination.

Contribution

It provides the first systematic analysis of spin and inclination constraints for XTE J2012+381 using multi-instrument spectral data and explores parameter uncertainties.

Findings

Black hole spin is consistently high across most parameter sets.

Inclination angle is well constrained between 50° and 65° in most cases.

Spectral modeling favors a reflection-Comptonization model.

Abstract

We present a spectral analysis of a black hole X-ray binary XTE J2012+381 during its 2022 outburst, using data from NICER and AstroSat. Combining data from NICER, LAXPC20, and SXT, we extract energy spectra covering the 0.7-10.0 keV range. We model the energy spectra using a series of physical models and find that a reflection-Comptonization model provides the best fit. Given the uncertainties in the black hole mass and source distance, we investigate the stability of the inferred spectral parameters by systematically varying the black hole mass (7.26, 11, and 16.5 M$_\odot$), source distance (3.3, 5.4, and 7.5 kpc), and spectral hardening factor (1.5, 1.7, and 1.9). We find that, across most combinations of these parameters, the spin solutions consistently lie in the high-spin regime, spanning values between $\sim$0.67 and $\sim$0.998, with only a limited subset of configurations favoring lower spins. In contrast, the disk inclination angle remains well constrained over the majority of the explored parameter space, typically ranging between $\sim$50{\deg} and $\sim$65{\deg}. Only a few parameter combinations yield higher inclination values.