Variable Short Optical Periods in SXP 4.78 (XTE J0052-723)
ATel #12920; P. C. Schmidtke (Arizona State University), A. P. Cowley (Arizona State University), A. Udalski (Warsaw University Observatory)
on 10 Jul 2019; 20:09 UT
Credential Certification: Paul Schmidtke (Paul.Schmidtke@asu.edu)
Subjects: Optical, X-ray, Binary, Neutron Star, Star, Pulsar
This source was identified as a new SMC X-ray transient by Coe et al. (ATel #12209) and designated as Swift J005139.2-721704. Soon after Strohmayer (ATel #12222) showed this source is the same as the pulsar XTE J0052-723 (SXP 4.78). Maravelias et al. (ATel #12237) obtained an optical spectral type of B1-2e for the optical counterpart. Using OGLE-III and -IV data Coe et al. (ATel #12229) identified an optical signal at 1.805 d, which they suggested may be the orbital period.
We have examined all 9 seasons of OGLE-IV data individually (see
http://ogle.astrouw.edu.pl/ogle4/xrom/sxp4.78.html ). The strongest periodic signals are present in Seasons 2 and 7, as shown in
http://www.public.asu.edu/~atpcs/SXP/SXP4.78_OGLEIV.pdf . The folded light curves for all periods are low-amplitude sinusoids. In Season 2 there is significant power at 0.5827 +/- 0.0014 d, with an alias at 1.399 +/- 0.009 d. Weaker signals at comparable periods were present in Season 1. No significant power was found in Seasons 3-6. Strong signals are present in Season 7 at 1.804 +/- 0.012 d (in agreement with the period found by Coe et al.) and 0.6425 +/- 0.0017 d, as shown in the figure. Similar but weaker features were also found in Season 8. There are insufficient data to find short periods in Season 9 due to an optical outburst that occurred during that season.
The changing periods and amplitudes indicate that the variations are not caused by orbital motion but are likely due to variable non-radial pulsations that are often found in Be stars.