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Identification of Short-period Optical Pulsations in IGR J01217-7257

ATel #5889; P. C. Schmidtke (Arizona State University), A. P. Cowley (Arizona State University), A. Udalski (Warsaw University Observatory)
on 14 Feb 2014; 21:23 UT
Credential Certification: Paul Schmidtke (Paul.Schmidtke@asu.edu)

Subjects: Optical, X-ray, Binary

Using INTEGRAL data, Coe et al. (2014, ATel #5806) recently discovered a bright X-ray source, IGR J01217-7257, in the SMC Wing. They identified the source with the 14th magnitude OGLE-IV star SMC732.03.3540. These authors found this star exhibits optical outbursts every 84 days when in its bright state. This is likely to be the orbital period of a new Be/X-ray binary. We note that the optical counterpart is coincident with the emission-line star [MA93]1888 (Meyssonnier & Azzopardi, 1993, A&AS, 102, 451) and is listed in SIMBAD as having a spectral type of B0-5II:e.

We have further examined four seasons of I-band photometry that are available from the XROM web site (Udalski, 2008, Acta Astron., 58, 187). After detrending the data by season, a refined long period of P=84.03 d was obtained using a phase dispersion minimization technique. The folded light curve is shown in the top panel of the attached figure (see URL link below). Since Be stars often show short-period pulsations, we searched the inter-outburst OGLE-IV data (between phases 0.1 and 0.9 of the 84-d period, as shown by the dashed box in the figure) for such pulsations. Periodogram analysis revealed optical pulsations at P=1.173 d with a full amplitude of ~0.02 mag, which are most prominent in seasons 2 and 3. The lower panel of the attached figure shows the lightcurve folded on this short period.

OGLE-IV light curve for IGR J01217-7257