EP J005146.9-730930: S-CUBED detection of a likely Be/XRB in the SMC
ATel #16796; J. A. Kennea, T. M. Gaudin (PSU), P. A. Evans (Leicester) and M. J. Coe (Southampton)
on 31 Aug 2024; 15:35 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Binary, Neutron Star, Transient
Xu et al (ATEL #16795) report on the discovery of a new X-ray transient in the SMC, EP J005146.9-730930 with Einstein Probe (EP). We have examined data from the Swift SMC Survey (S-CUBED; Kennea et al, 2018), to confirm this new presence.
We find an uncatalogued X-ray source with rising brightness detected in the survey starting July 30th, 2024, with subsequent detections on August 13th, 20th and 27th. The source has the following coordinates: RA/Dec(J2000) = 12.94594, -73.15658 which is equivalent to:
RA(J2000) = 00h 51m 47.03s
Dec(J2000) = -73d 09m 23.7s
with an estimated uncertainty of 3.6 arc-seconds radius (90% confidence). This position lies 4.5 arc-seconds from the reported EP position, and 2.8 arc-seconds from the optical source OGLE J005147.58-730924.7, which is reported to be a candidate Be star (Mennickent et al, 2002, 393, 887). The Swift localization is consistent with both sources, so we suggest that EP J005146.9-730930 is likely a newly discovered Be/XRB.
The light-curve over four detections shows variability, with the source brightest on August 13th, 2023 with a count rate of 1.1 +/- 0.3 XRT count/s. The spectrum is fit by a power-law with average photon index 0.4 +/- 0.5, consistent with hard X-ray spectrum expected from a Be/XRB with a neutron star compact object.
In historical S-CUBED data we see previous detections of this source, however this is the first outburst since S-CUBED began in June 2016.
