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arXiv · 2602.07459

SXP 31.0 -- the 2025 near-Eddington double X-ray outburst after 26 years of quiescence

Malcolm J. Coe·Thomas M. Gaudin·Itumeleng M. Monageng·Jamie A. Kennea·David A. H. Buckley·Andrzej Udalski·Phil A. Evans·Sabyasachi Chattopadhyay
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Abstract

SXP 31.0 is an X-ray source in the Small Magellanic Cloud (SMC) that was first identified as a Be X-ray Binary (BeXRB) system when it went into X-ray outbusrst in 1998. It is now known to consist of an OBe main sequence star and a neutron star with a spin period of 31s. In 2025 a new X-ray outburst phase began with the source exhibiting a luminosities approaching the Eddington limit of 10^38 erg/s. Unusually, H-alpha images show it has a surrounding halo whose nature has not been clear. In this paper, we report new observations of this halo, including the first multi-fibre Integrated Flux Unit (IFU) observations, which identify this emission as probably a coincidental HII region. The X-ray, UV & optical data cover a period of ~200d and reveal that the source underwent two bright, back-to-back, Type II outbursts in 2025 - a rare occurrence for any BeXRB system.

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Malcolm J. Coe, Thomas M. Gaudin, Itumeleng M. Monageng, Jamie A. Kennea, David A. H. Buckley, Andrzej Udalski, Phil A. Evans, Sabyasachi Chattopadhyay. 2026-02-07. SXP 31.0 -- the 2025 near-Eddington double X-ray outburst after 26 years of quiescence. https://arxiv.org/abs/2602.07459

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