Short-period Optical Pulsations in Swift J010745.0-722740
ATel #5781; P. C. Schmidtke (Arizona State University), A. P. Cowley (Arizona State University), A. Udalski (Warsaw University Observatory)
on 20 Jan 2014; 22:45 UT
Credential Certification: Paul Schmidtke (Paul.Schmidtke@asu.edu)
Subjects: Optical, X-ray, Binary
Referred to by ATel #: 14724
Recently, Maggi et al. (ATel #5778) announced the discovery that Swift J010745.0-722740 is a new SMC Be/X-ray binary which undergoes prominent optical outbursts (~0.5 mag) about every 1180 d. They identify the optical counterpart as emission-line star [MA93]1641. OGLE-IV observations show the quiescent magnitude of the system is I~15.1 but with considerable scatter. We have analyzed the data between outbursts looking for possible short-term periodicities. There are very strong optical pulsations with P=0.3504+/-0.0001 d. A similar period of P=0.3500+/-0.0001 d is found in OGLE-II data (star sc11_53243). The folded light curve from each data set is sinusoidal with a full amplitude of about ~0.04 mag. Such short pulsation periods are seen in many other Be/X-ray systems (e.g. Schmidtke, Cowley, & Udalski, 2013 MNRAS, 431, 252).
In addition, we note that the strong 1180-d orbital outbursts are double peaked. The link below is to a plot showing the outbursts from OGLE-II and -IV data. Doubled-peaked outbursts like these are seen in several other SMC Be/X-ray systems (e.g. SXP 7.78, SMC X-3, SXP46.6, SXP291, and SXP327).
Optical Outbursts for Swift J010745.0-722740
