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

M. J. Coe; T. M. Gaudin; I. M. Monageng; J. A. Kennea; D. A.H. Buckley; A. Udalski; P. A. Evans; S. Chattopadhyay

doi:10.1093/mnras/stag265

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

M. J. Coe
, T. M. Gaudin
, I. M. Monageng
, J. A. Kennea
, D. A.H. Buckley
, A. Udalski
, P. A. Evans
, S. Chattopadhyay

Astronomy & Astrophysics

Research output: Contribution to journal › Article › peer-review

Abstract

SXP 31.0 is an X-ray source in the Small Magellanic Cloud 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 10³⁸ ergs⁻¹. Unusually, H α 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 multifibre Integrated Flux Unit observations, which identify this emission as probably a coincidental Hii region. The X-ray, UV, and 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.

Original language	English (US)
Article number	stag265
Journal	Monthly Notices of the Royal Astronomical Society
Volume	546
Issue number	4
DOIs	https://doi.org/10.1093/mnras/stag265
State	Published - Mar 1 2026

All Science Journal Classification (ASJC) codes

Astronomy and Astrophysics
Space and Planetary Science

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10.1093/mnras/stag265

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

abstract = "SXP 31.0 is an X-ray source in the Small Magellanic Cloud 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 1038 ergs−1. Unusually, H α 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 multifibre Integrated Flux Unit observations, which identify this emission as probably a coincidental Hii region. The X-ray, UV, and optical data cover a period of \textasciitilde{}200d and reveal that the source underwent two bright, back-to-back, Type II outbursts in 2025-a rare occurrence for any BeXRB system.",

author = "Coe, \{M. J.\} and Gaudin, \{T. M.\} and Monageng, \{I. M.\} and Kennea, \{J. A.\} and Buckley, \{D. A.H.\} and A. Udalski and Evans, \{P. A.\} and S. Chattopadhyay",

note = "Publisher Copyright: {\textcopyright} The Author(s) 2026. Published by Oxford University Press on behalf of Royal Astronomical Society.",

year = "2026",

month = mar,

day = "1",

doi = "10.1093/mnras/stag265",

language = "English (US)",

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T1 - SXP 31.0-the 2025 near-Eddington double X-ray outburst after 26years of quiescence

AU - Coe, M. J.

AU - Gaudin, T. M.

AU - Monageng, I. M.

AU - Kennea, J. A.

AU - Buckley, D. A.H.

AU - Udalski, A.

AU - Evans, P. A.

AU - Chattopadhyay, S.

PY - 2026/3/1

Y1 - 2026/3/1

N2 - SXP 31.0 is an X-ray source in the Small Magellanic Cloud 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 1038 ergs−1. Unusually, H α 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 multifibre Integrated Flux Unit observations, which identify this emission as probably a coincidental Hii region. The X-ray, UV, and 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.

AB - SXP 31.0 is an X-ray source in the Small Magellanic Cloud 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 1038 ergs−1. Unusually, H α 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 multifibre Integrated Flux Unit observations, which identify this emission as probably a coincidental Hii region. The X-ray, UV, and 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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DO - 10.1093/mnras/stag265

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SN - 0035-8711

VL - 546

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 4

M1 - stag265

ER -

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

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