CXOU J005245.0-722844: Optical period of possible counterpart hints at BeXRB nature of the system
ATel #16638; H. Treiber (Princeton), F. Haberl (MPE), G. Vasilopoulos (NKUA), C. D. Bailyn (Yale), A. Udalski (Warsaw University Observatory)
on 4 Jun 2024; 21:50 UT
Credential Certification: Georgios Vasilopoulos (gevas@phys.uoa.gr)
Subjects: Optical, X-ray, Binary, Transient
An X-ray outburst was recently detected by the Einstein Probe mission and designated EP J0052.9-7230 (ATel #16631). Swift's S-CUBED survey (Kennea et al. 2018) then localized the event to the X-ray source CXOU J005245.0-722844 and noted that the soft spectrum is consistent with a Be X-ray binary (BeXRB) system with a white dwarf as the compact object (ATel #16633). NICER observations further supported this interpretation (ATel #16636).
The optical counterpart (RA = 0:52:45.10, Dec = -72:28:43.7) to this system has been monitored by the Optical Gravitational Lensing Experiment (OGLE) for 23 years. We report the optical properties of this system, which we discuss in more detail in an upcoming publication (Treiber et al., in preparation).
The optical counterpart (OGLE IV I-band ID smc719.20.104) has a mean I magnitude of 14.85 mag and a standard deviation of 0.04 mag. A Lomb-Scargle periodogram of the I-band data reveals a strong peak at 17.55 days, consistent with the potential orbital periodicity determined from MACHO data (Sarraj et al. 2012 IBVS, 6030, 1S). This peak is clearly apparent with or without detrending of the low-level longer-term variability. The signal is persistent throughout the light curve, with the exception of ~1500 days (2015-2020). We also note that the OGLE V-band data reveals a significant redder-when-brighter relation, albeit with extensive scatter, which is characteristic of BeXRB systems. Furthermore, despite the lower V-band coverage (i.e., 158 observations), the same periodicity peak appears in V-I.
