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’ states, 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 XTE J1752-223 being a stellar mass black hole accretor and not a neutron star. Physically motivated and self-consistent reflection models for the Fe Kα emission-line profile and disc reflection spectrum rule out either a non-rotating, Schwarzschild black hole or a maximally rotating, Kerr black hole at greater than 3σ 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 ± 0.11(1σ). Furthermore, we show that the source in the low-hard state still requires an optically thick disc component having a luminosity which is consistent with the L∝T4 relation expected for a thin disc extending down to the innermost stable circular orbit. Our result is in contrast to the prevailing paradigm that the disc is truncated in the low-hard state.
Cosmology, Relativity, and Gravity | Stars, Interstellar Medium and the Galaxy
Reis, R. C., Miller, J. M., Fabian, A. C., Cackett, E. M., Maitra, D., Reynolds, C. S., Rupen, M., Steeghs, D. T. H., Wijnands, R. 2011. Multistate observations of the Galactic black hole XTE J1752-223: evidence for an intermediate black hole spin. MNRAS 410(4), 2497-2505.