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High-mass X-ray binary SXP18.3 undergoes the longest type II outburst ever seen in the Small Magellanic Cloud |
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| Authors: | M P E Schurch M J Coe J L Galache R H D Corbet K E McGowan V A McBride L J Townsend A Udalski F Haberl |
| Institution: | School of Physics and Astronomy, Southampton University, Highfield, Southampton, SO17 1BJ;Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA;University of Maryland Baltimore County, X-ray Astrophysics Laboratory, Mail Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA;Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warsaw, Poland;Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748, Germany |
| Abstract: | On 2006 August 30, SXP18.3 a high-mass X-ray binary (HMXB) in the Small Magellanic Cloud (SMC) with an 18.3 s pulse period was observed by Rossi X-ray Timing Explorer ( RXTE ). The source was seen continuously for the following 36 weeks. This is the longest type II outburst ever seen from a HMXB in the SMC. During the outburst, SXP18.3 was located from serendipitous XMM–Newton observations. The identification of the optical counterpart has allowed SXP18.3 to be classified as a Be/X-ray binary. This paper will report on the analysis of the optical and weekly RXTE X-ray data that span the last 10 yr. The extreme length of this outburst has for the first time enabled us to perform an extensive study of the pulse timing of a SMC Be/X-ray binary. We present a possible full orbital solution from the pulse timing data. An orbital period of 17.79 d is proposed from the analysis of the Optical Gravitational Lensing Experiment (OGLE) III light curve placing SXP18.3 on the boundary of known sources in the Corbet diagram. |
| Keywords: | stars: emission-line Be Magellanic Clouds X-rays: binaries |