arXiv subjects

Thomas M. Gaudin

Publications and source records attributed to Thomas M. Gaudin.

4 recordsLinked to original sources

arXiv2026

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

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.

astro-ph.SR↗

arXiv2025

Identification of New Candidate Be/X-Ray Binary Systems in the Small Magellanic Cloud via Analysis of S-CUBED Source Catalog

It has long been known that a large population of Be/X-ray Binaries (BeXRBs) exists in the Milky Way's neighboring dwarf galaxy, the Small Magellanic Cloud (SMC), due to a recent period of intense star formation. Since 2016, efforts have been made to monitor this population and identify new BeXRBs through the Swift SMC Survey (S-CUBED). S-CUBED's weekly observation cadence has identified many new BeXRBs that exist within the SMC, but evidence suggests that more systems exist that have thusfar escaped detection. A major challenge in identifying new BeXRBs is their transient nature at high-energy wavelengths, which prevents them from being detected via their X-ray emission characteristics when not in outburst. In order to identify sources that may have been missed due to a long period of quiescence, it becomes necessary to devise methods of detection that rely on wavelengths at which BeXRBs are more persistent emitters. In this work, we attempt to use archival analysis of infrared, optical, and ultraviolet observations to identify new candidate BeXRBs that have been overlooked within the S-CUBED source catalog. Using X-ray/optical selection of source properties, unsupervised clustering, SED-fitting to VizieR archival measurements, and ultraviolet light curve analysis, we are able to identify six new candidate BeXRB systems that otherwise would have been missed by automated analysis pipelines. Using these results, we demonstrate the use of ultraviolet through near-infrared observational data in identifying candidate BeXRBs when they cannot be identified using their X-ray emission.

astro-ph.HE↗

arXiv2024

CXOU J005245.0-722844: Discovery of a Be Star / White Dwarf binary system in the SMC via a very fast, super-Eddington X-ray outburst event

CXOU J005245.0-722844 is an X-ray source in the Small Magellanic Cloud (SMC) that has long been known as a Be/X-ray binary (BeXRB) star, containing an OBe main sequence star and a compact object. In this paper, we report on a new very fast X-ray outburst from CXOU J005245.0-722844. X-ray observations taken by Swift constrain the duration of the outburst to less than 16 days and find that the source reached super-Eddington X-ray luminosities during the initial phases of the eruption. The XRT spectrum of CXOU J005245.0-722844 during this outburst reveals a super-soft X-ray source, best fit by an absorbed thermal blackbody model. Optical and Ultraviolet follow-up observations from the Optical Gravitational Lensing Experiment (OGLE), Asteroid Terrestrial-impact Last Alert System (ATLAS), and Swift identify a brief ~0.5 magnitude optical burst coincident with the X-ray outburst that lasted for less than 7 days. Optical photometry additionally identifies the orbital period of the system to be 17.55 days and identifies a shortening of the period to 17.14 days in the years leading up to the outburst. Optical spectroscopy from the Southern African Large Telescope (SALT) confirms that the optical companion is an early-type OBe star. We conclude from our observations that the compact object in this system is a white dwarf (WD), making this the seventh candidate Be/WD X-ray binary. The X-ray outburst is found to be the result of a very-fast, ultra-luminous nova similar to the outburst of MAXI J0158-744.

astro-ph.HE↗

arXiv2024

Discovery of a Rare Eclipsing Be/X-ray Binary System, Swift J010902.6-723710 = SXP 182

We report on the discovery of Swift J010902.6-723710, a rare eclipsing Be/X-ray Binary system by the Swift SMC Survey (S-CUBED). Swift J010902.6-723710 was discovered via weekly S-CUBED monitoring observations when it was observed to enter a state of X-ray outburst on 10 October 2023. X-ray emission was found to be modulated by a 182s period. Optical spectroscopy is used to confirm the presence of a highly-inclined circumstellar disk surrounding a B0-0.5Ve optical companion. Historical UV and IR photometry are then used to identify strong eclipse-like features re-occurring in both light curves with a 60.623 day period, which is adopted as the orbital period of the system. Eclipsing behavior is found to be the result of a large accretion disk surrounding the neutron star. Eclipses are produced when the disk passes in front of the OBe companion, blocking light from both the stellar surface and circumstellar disk. This is only the third Be/X-ray Binary to have confirmed eclipses. We note that this rare behavior provides an important opportunity to constrain the physical parameters of a Be/X-ray Binary with greater accuracy than is possible in non-eclipsing systems.

astro-ph.HE↗