S-CUBED Detects SXP 31.0 in Outburst for the First Time
ATel #17147; T. M. Gaudin (PSU), J. A. Kennea (PSU), M. J. Coe (Southampton University, UK), P. Evans (Leicester University, UK)
on 15 Apr 2025; 16:30 UT
Credential Certification: Thomas Gaudin (tmg6006@psu.edu)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The Be/X-ray Binary system SXP 31.0 has been detected by a Swift SMC Survey (S-CUBED) observation for the first time since regular shallow monitoring of the Small Magellanic Cloud first began in 2016. This detection occurred during the observation taken at 00:45 UTC on 15 April 2025 when the source was detected at an X-ray luminosity of 1.75 x 10^37 erg/s (~0.38 counts/sec in the 0.3-10 keV Swift XRT band). The Enhanced Swift XRT position of the source is RA (J2000): 01h 11m 09.51s (17.78962), Dec (J2000): -73° 16' 44.9" (-73.27915) with a 90% confidence error region of 6.3".
A bright optical source has been found inside the XRT error region for SXP 31.0. This optical source is consistent with the position of 2MASS J01110860-7316462, which was reported by Covino et al. (2001) to be the optical counterpart to the X-ray source.
This source is largely a quiescent Be/X-ray Binary that exhibits quasi-periodic oscillations at X-ray wavelengths (Kaur et al., 2007). Based on reports of surrounding nebular emission, it has been speculated that the source likely resides in a supernova remnant (Coe et al., 2000). The source was not detected in a previous S-CUBED observation obtained on 11 March 2025. The last confirmed detection for the source was its original discovery in 1998 by RXTE (Chakrabarty et al., 1998a). Follow-up observations have been requested from both NICER and Swift. Other follow-up observations are encouraged at all wavelengths.
