Swift detection of an X-ray outburst from the SMC transient SXP 202A

ATel #9307; M. J. Coe (Southampton), P. A. Evans (Leicester), J. A. Kennea (PSU) & A. Udalski (Warsaw)
on 3 Aug 2016; 16:02 UT
Credential Certification: Malcolm Coe (mjcoe@soton.ac.uk)

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We report on the results from the Swift SMC Survey (S-CUBED), a wide area/short exposure survey of the SMC in X-rays performed by the Swift X-ray Telescope (XRT); see ATel #9299 for programme details. S-CUBED observations taken over the period MJD 57575 to 57600 reveal an X-ray outburst from the Be/X-ray binary system, SXP 202A (Majid et al Ap J 609, 133, 2004) lasting approximately 25 days. The flux peaked at 0.3 +/- 0.1 counts/s in the XRT telescope suggesting an intrinsic X-ray luminosity of (4 +/- 1.5) x 10^36 erg/s (assuming the source is in the SMC with power law emission of a photon index 1.5). This is an order of magnitude brighter than the previous reported detections of this source which have been in the (4-6) x 10^35 erg/s range (Eger & Haberl A&A 491, 841, 2008). The source has been detected on many previous occasions by Swift, but at a flux level of approximately a factor of five below the current level. Hence the current activity is clearly a unusually large outburst. OGLE IV data taken on MJD 57568 do not show any particular rise in the I-band flux suggesting that, despite the increased X-ray luminosity, the X-ray outburst may be a larger than average Type I event occurring whilst the neutron star was near periastron. The binary period for SXP 202A is currently unknown, but the Corbet diagram suggests a value around 200 days. We will continue to monitor this object with the S-CUBED programme to look for further outbursts that may help identify the orbital period and improve our understanding of the nature of the current outburst.