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Orbital period detected in new SMC Be/X-ray binary XMMU J005929.0-723703

ATEL # 1611; M.P.E. Schurch (Southampton University) A. Udalski (Warsaw
on 9 Jul 2008; 18:40 UT
Password Certification: Malcolm Coe (mjcoe@soton.ac.uk)

Subjects: Optical, X-ray, Binaries, Neutron Stars, Pulsars, Transients

The OGLE III optical data (object SMC105.3-29894) of the Be star counterpart to the newly discovered SMC transient X-ray source XMMU J005929.0-723703 (Haberl et al. 2008, 2008arXiv0806.4132) shows 8 clear optical outbursts with a typical increase in I band magnitude of 0.4mag. The data were first detrended to remove the very long term global changes. Lomb-Scargle analysis reveals a strong coherent periodicity of 229.9 +/- 0.9 days. Haberl et al. (2008) find a weak signal in the analysis of MACHO R-band data at 220 days. This period combined with the pulse period (202s) places the source directly in the centre of the distribution of Be/X-ray binaries on the Corbet diagram. We thus propose the binary period of the system to be 229.9d with an ephemeris of MJD 51985.8.


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