Swift J004516.6-734703 = SXP146.6: A newly discovered BeXRB in the SMC
ATel #13823; J. A. Kennea (PSU), M. J. Coe (Soton), P. A. Evans (Leicester), I. M. Monageng (SAAO/Cape Town), L. J. Townsend (SAAO), M. H. Siegel (PSU), A. Udalski (Warsaw), D. A. H. Buckley (SAAO)
on 22 Jun 2020; 19:10 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Neutron Star, Star, Pulsar
We report on the detection on June 18, 2020 by S-CUBED, a weekly survey of the SMC by the Neil Gehrels Swift Observatory, of a new transient X-ray source in the SMC at the following coordinates: RA/Dec (J2000) = 11.32462, -73.78485, which is equivalent to
RA(J2000) =00h 45m 17.91s,
Dec(J2000) = -73d 47m 05.5s,
with an estimated error radius of 1.9 arc-seconds (90% confidence). Follow-up TOO observations of this object, Swift J004516.6-734703, were performed, and we find that the source was rising in brightness, with a peak luminosity (assuming a standard SMC distance) of 1.5 x 1037 erg/s (0.5-10 keV). Analysis of the PC mode data showed that the spectrum was hard (photon index = 0.5 +/- 0.16), typical of accreting pulsars. Timing analysis of the PC data shows a strong detection of a 146s pulsar period, further confirming its nature as an accreting pulsar.
The X-ray position is consistent with an optical counterpart, 2dFS0556, which is classified by Evans et al. (2004) as a B1-3(III) spectral type star. We performed observations with SALT to obtain a spectrum, which revealed the presence of strong H-alpha emission line, confirming that that the companion was a Be-star, and that Swift J004516.6-734703, AKA SXP 146.6, is a previously unknown Be/X-ray Binary. Timing analysis of the OGLE III & IV data reveal a clear period of 426d which we interpret as a possible binary period.
A full report on this new object has been submitted to MNRAS (Kennea et al., 2020) and will appear on arXiv.org soon.
