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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


NOTICE IN COMPLIANCE WITH PUBLISHER POLICY: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2011 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved. Available at doi:10.1111/j.1365-2966.2010.17628.x