S-CUBED Detects a new outburst of the Be/X-ray binary SXP 8.80

ATel #17246; T. M. Gaudin (PSU), J. A. Kennea (PSU), M. J. Coe (Southampton University, UK), A. Udalski (Warsaw University, Poland), P. A. Evans (Leicester University, UK)
on 26 Jun 2025; 13:41 UT
Credential Certification: Thomas Gaudin (tmg6006@psu.edu)

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An observation as part of the regular weekly Swift SMC Survey (S-CUBED, Kennea et al 2018) has detected the Be/X-ray Binary SXP 8.80 with the X-ray Telescope (XRT) for the first time in almost two years. The observation conducted at 01:29 UTC on 24 June 2025 detected the source at an X-ray luminosity of 1.4 x 10^37 erg/s (~0.65 counts/sec in the 0.3-10 keV Swift XRT band). A follow-up, deeper observation taken by Swift later in the day at 16:46 UTC revealed that the source has increased in brightness to an X-ray luminosity of 2.3 x 10^37 erg/s (~0.7 counts/sec). The Enhanced Swift XRT position of the source can be derived from the follow-up observation. This position is RA (J2000): 00h 51m 52.99s (12.97078), Dec (J2000): -72° 31' 48.6" (-72.53017) with a 90% confidence error region of 2.3".

Simultaneous UV/Optical Telescope (UVOT) observations reveal a bright UV/optical source within the XRT error region that corresponds to the position of the agreed counterpart MA93 506 to SXP 8.80 (Haberl F. & Sasaki M., 2000).

This source has been observed to go into outburst before by S-CUBED. The last outburst was detected over a period of 35 days in October and November 2023, reaching a maximum X-ray luminosity of 1.81 x 10^37 erg/s on 31 October 2023. Regular historical monitoring by the Optical Gravitational Lensing Experiment (OGLE) indicates that the source (OGLE SMC 719.12.35646) undergoes irregular, large optical "flares" during which the source can increase in I-band magnitude by as much as 0.75 magnitudes that can coincide with the timing of X-ray outbursts. Recent observations of OGLE indicate that the source is undergoing such a flare now and is measured to be at an I-band magnitude of ~14.35. An OGLE light curve for the source can be found at the X-Ray variables OGLE Monitoring (XROM) website (https://ogle.astrouw.edu.pl/ogle4/xrom/sxp8.80.html). Follow-up observations have been requested by Swift. Other follow-up observations are encouraged at all wavelengths.

X-Ray variables OGLE Monitoring (XROM) website