Multi-state observations of the Galactic Black Hole XTE J1752-223: Evidence for an intermediate black hole spin

TL;DR

This study analyzes XTE J1752-223 during its 2009 outburst decay, using X-ray spectra to measure the black hole's spin and disk properties, challenging the idea that disks are truncated in the low-hard state.

Contribution

The paper provides the first robust measurement of the black hole spin in XTE J1752-223 and shows the presence of an optically-thick disk in the low-hard state, contradicting previous models.

Findings

Black hole spin parameter constrained to 0.52 ± 0.11.

Relativistic iron emission line detected in both states.

Disk extends to the innermost stable orbit in the low-hard state.

Abstract

The Galactic Black hole candidate XTE J1752-223 was observed during the decay of its 2009 outburst with the Suzaku and XMM-Newton observatories. The observed spectra are consistent with the source being in the ''intermediate`` and ''low-hard state`` respectively. The presence of a strong, relativistic iron emission line is clearly detected in both observations and the line profiles are found to be remarkably consistent and robust to a variety of continuum models. This strongly points to the compact object in \j\ being a stellar-mass black hole accretor and not a neutron star. Physically-motivated and self-consistent reflection models for the Fe-\ka\ emission-line profile and disk reflection spectrum rule out either a non-rotating, Schwarzchild black hole or a maximally rotating, Kerr black hole at greater than 3sigma level of confidence. Using a fully relativistic line function in which the black hole spin parameter is a variable, we have formally constrained the spin parameter to be $0.52\pm0.11 (1\sigma)$. Furthermore, we show that the source in the low--hard state still requires an optically--thick disk component having a luminosity which is consistent with the $L\propto T^4$ relation expected for a thin disk extending down to the inner--most stable circular orbit. Our result is in contrast to the prevailing paradigm that the disk is truncated in the low-hard state.