Einstein Probe Discovery of EP J005245.1−722843: A Rare Be–White Dwarf Binary in the Small Magellanic Cloud?

Einstein Probe Discovery of EP J005245.1−722843: A Rare Be–White Dwarf Binary in the Small Magellanic Cloud?

On 2024 May 27, the Wide-field X-ray Telescope on board the Space Sciences, University of Chinese Academy of Einstein Probe (EP) mission detected enhanced X-ray emission from a new transient source in the Small Magellanic Cloud during its commissioning phase. Prompt follow-up with the EP Follow-up X...

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Main Authors: A. Marino, H. N. Yang, F. Coti Zelati, N. Rea, S. Guillot, G. K. Jaisawal, C. Maitra, J.-U. Ness, F. Haberl, E. Kuulkers, W. Yuan, H. Feng, L. Tao, C. Jin, H. Sun, W. Zhang, W. Chen, E. P. J. van den Heuvel, R. Soria, B. Zhang, S.-S. Weng, L. Ji, G. B. Zhang, X. Pan, Z. Lv, C. Zhang, Z. X. Ling, Y. Chen, S. Jia, Y. Liu, H. Q. Cheng, D. Y. Li, K. Gendreau, M. Ng, T. Strohmayer
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal Letters
Subjects:
Accretion
X-ray binary stars
High mass x-ray binary stars
White dwarf stars
Small Magellanic Cloud
Online Access:https://doi.org/10.3847/2041-8213/ad9580
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Summary:On 2024 May 27, the Wide-field X-ray Telescope on board the Space Sciences, University of Chinese Academy of Einstein Probe (EP) mission detected enhanced X-ray emission from a new transient source in the Small Magellanic Cloud during its commissioning phase. Prompt follow-up with the EP Follow-up X-ray Telescope, the Swift X-ray Telescope. and NICER have revealed a very soft, thermally emitting source ( kT  ~ 0.1 keV at the outburst peak) with an X-ray luminosity of L  ~ 4 × 10 ^38 erg s ^−1 , labeled EP J005245.1−722843. This supersoft outburst faded very quickly in a week's time. Several emission lines and absorption edges were present in the X-ray spectrum, including deep nitrogen (0.67 keV) and oxygen (0.87 keV) absorption edges. The X-ray emission resembles the supersoft source phase of typical nova outbursts from an accreting white dwarf (WD) in a binary system, despite the X-ray source being historically associated with an O9-B0e massive star exhibiting a 17.55 day periodicity in the optical band. The discovery of this supersoft outburst suggests that EP J005245.1−722843 is a BeWD X-ray binary: an elusive evolutionary stage where two main-sequence massive stars have undergone a common envelope phase and experienced at least two episodes of mass transfer. In addition, the very short duration of the outburst and the presence of Ne features hint at a rather massive, i.e., close to the Chandrasekhar limit, Ne–O WD in the system.
ISSN:2041-8205

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