Be/X-ray binary SXP6.85 undergoes large type II outburst in the small magellanic cloud

Townsend, L.J., Coe, M.J., McBride, V.A., Bird, A.J., Schurch, M.P.E., Corbet, R.H.D., Haberl, F., Galache, J.L. and Udalski, A. (2010) Be/X-ray binary SXP6.85 undergoes large type II outburst in the small magellanic cloud. Monthly Notices of the Royal Astronomical Society, 403 (3), 1239-1245. (doi:10.1111/j.1365-2966.2009.16211.x).

Abstract

The Small Magellanic Cloud (SMC) Be/X-ray binary pulsar SXP6.85 = XTE J0103?728 underwent a large Type II outburst beginning on 2008 August 10. The source was consistently seen for the following 20 weeks (MJD = 54688–54830). We present X-ray timing and spectroscopic analysis of the source as a part of our ongoing Rossi X-ray Timing Explorer (RXTE) monitoring campaign and INTEGRAL key programme monitoring the SMC and 47 Tuc. A comparison with the Optical Gravitational Lensing Experiment (OGLE) III light curve of the Be counterpart shows the X-ray outbursts from this source coincide with times of optical maximum. We attribute this to the circumstellar disc increasing in size, causing mass accretion on to the neutron star. Ground based infrared photometry and H? spectroscopy obtained during the outburst are used as a measure of the size of the circumstellar disc and lend support to this picture. In addition, folded RXTE light curves seem to indicate complex changes in the geometry of the accretion regions on the surface of the neutron star, which may be indicative of an inhomogeneous density distribution in the circumstellar material causing a variable accretion rate on to the neutron star. Finally, the assumed inclination of the system and H? equivalent width measurements are used to make a simplistic estimate of the size of the circumstellar disc.

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Contributors

Author: M.J. Coe

Author: A.J. Bird

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