Astrophys. J., 778, 155 (2013/December-1)
SWIFT J1910.2-0546: a possible black hole binary with a retrograde spin or truncated disk.
REIS R.C., REYNOLDS M.T., MILLER J.M., WALTON D.J., MAITRA D., KING A. and DEGENAAR N.
Abstract (from CDS):
We present the first results from a long (51 ks) XMM-Newton observation of the Galactic X-ray binary SWIFT J1910.2-0546 in an intermediate state, obtained during its 2012 outburst. A clear, asymmetric iron emission line is observed and physically motivated models are used to fully describe the emission-line profile. Unlike other sources in their intermediate spectral states, the inner accretion disk in SWIFT J1910.2-0546 appears to be truncated, with an inner radius of rin9.4–1.3+1.7 rg at a 90% confidence limit. Quasi-periodic oscillations are also found at approximately 4.5 and 6 Hz, which correlates well with the break frequency of the underlying broad-band noise. Assuming that the line emission traces the innermost stable circular orbit, as would generally be expected for an intermediate state, the current observation of SWIFT J1910.2-0546 may offer the best evidence for a possible retrograde stellar mass black hole with a spin parameter a < - 0.32cJ/GM2 (90% confidence). Although this is an intriguing possibility, there are also a number of alternative scenarios which do not require a retrograde spin. For example, the inner accretion disk may be truncated at an unusually high luminosity in this case, potentially suffering frequent evaporation/condensation, or it could instead be persistently evacuated through mass loss in a relativistic jet. Further observations are required to distinguish between these different interpretations.
accretion, accretion disks - relativistic processes - X-rays: binaries - X-rays: individual: SWIFT J1910.2-0546
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