XMM-Newton detection of a bright outburst from the accreting pulsar 1A 0538-66
ATel #17455; L. Ducci (University of Tuebingen), S. Mereghetti (INAF/IASF-Milano), M. Bachetti (INAF-OACagliari)
on 27 Oct 2025; 11:41 UT
Credential Certification: Lorenzo Ducci (ducci@astro.uni-tuebingen.de)
Subjects: X-ray, Neutron Star, Transient, Pulsar
We report on the detection of a bright X-ray outburst from the Be/X-ray binary 1A 0538-66 in the Large Magellanic Cloud with XMM-Newton. We observed the source on 2025-09-30, from 13:58:29 UTC to 17:54:56 UTC (exposure time: ~14 ks).
A preliminary analysis of EPIC-pn data indicates relatively stable emission throughout the observation. The source flux in 0.2-12 keV band was ~5e-9 erg/cm^2/s. At the assumed distance of 50 kpc, this corresponds to a luminosity of ~1.5e39 erg/s, significantly exceeding the Eddington limit of a neutron star. This is the highest luminosity observed from 1A 0538-66 since its giant outbursts in 1980 (Skinner et al. 1982 Nature, 297, 568).
Preliminary timing analysis of the pn data revealed X-ray pulsations at a period of ~69.5 ms.
The spectrum, which is affected by strong pile-up, can be described by an absorbed model with two-powerlaw components (N_H ~ 1.5e21 cm^-2, Gamma_1 ~ 1.4; Gamma_2 ~ 2.9), that is with a spectral shape similar to that in previous XMM-Newton observations of 2018 (Ducci, Mereghetti, and Santangelo 2019, ApJL 881 17).
We encourage multi-wavelengths follow up observations. 1A 0538-66 is known to exhibit bright and optical flaring in correlation with its X-ray outbursts (e.g., Ducci et al. 2022 A&A 661 22), making it a prime target for coordinated campaigns with optical telescopes.
