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SXP 15.3 and SXP 305 are two Be X-ray binaries in the Small Magellanic Cloudthat are spatially separated by ~7 arcsec. The small separation between thesesources has, in the past, resulted in confusion about the origin of theemission from the combined region. We present long-term optical and X-raymonitoring results of both sources, where we study the historic and recentbehaviour. In particular, from data collected as part of the S-CUBED project wesee repeating X-ray outbursts from the combined region of the two sources inthe recent lightcurve from the Neil Gehrels Swift Observatory, and weinvestigate the origin of this emission. Using the H-alpha emission line fromthe Southern African Large Telescope (SALT) and photometric flux from theOptical Gravitational Lensing Experiment (OGLE) to study the changes in thesize and structure of the Be disc, we demonstrate that the X-ray emissionlikely originates from SXP 15.3. Timing analysis reveals unusual behaviour,where the optical outburst profile shows modulation at twice the frequency ofthe X-ray outbursts. We consider either of these periodicities being the trueorbital period in SXP 15.3 and propose models based on the geometricorientations of the Be disc and neutron star to explain the physical origin ofthe outbursts.

Disentangling the neighbouring pulsars SXP 15.3 and SXP 305