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ATEL # 1953; P. C. Schmidtke (Arizona State University), A. P. Cowley (Arizona State University), A. Udalski (Warsaw University Observatory)
on 6 Mar 2009; 20:18 UT
Password Certification: Paul Schmidtke (Paul.Schmidtke@asu.edu)
Subjects: Optical, X-ray, Binaries, Neutron Stars, Pulsars
We have analyzed 8 seasons of OGLE-III data for SXP967 (formerly SXP700; see discussion of the revised pulsar period by Haberl et al., 2008, A&A 489, 327). The I-band observations show long-term changes of 0.6 mag, which were removed via polynomial fitting to long segments of data (1-3 seasons in length). The remaining small-amplitude variations were analyzed using both periodogram and PDM techniques. The strongest signal, with P=101.94 days, has an asymmetrical shape (very rapid rise followed by gradual decline over 0.2P) with an amplitude of nearly 0.1 mag. The recurrence time and shape of these outbursts suggests they are caused by orbital motion of the Be/pulsar binary. Examination of inter-outburst data shows strong power in the periodogram at P=1.003 days. The folded light curve is sinusoidal with full amplitude of ~0.02 mag, suggesting the variation is due to non-radial pulsations (NRP) of the Be star. These appear to be stable throughout the observations. An alias of the pulsation period (at P~258 days) shows less power, and its sinusoidal light curve argues against it being the orbital period. We note that McGowan et al. (2007, MNRAS 376, 759) reported a 267-day period using 5 seasons of OGLE-III data, consistent with also being an alias of the NRP.