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Updated: Apr 14, 2026

Setting Limits on Supersymmetry Using Simplified Models
Published on: November 15, 2013
The first extragalactic ultra-compact X-ray binary: A candidate black hole-white dwarf system
Qian-Qi Ma1, Jiachang Zhang2,3, Wei-Min Gu1
1Department of Astronomy, Xiamen University, Xiamen, Fujian 361005, China.
Abstract:
M31 UCXB-1 is one of the brightest X-ray point sources in the bulge of M31, with a peak X-ray luminosity . Both XMM-Newton and Chandra observations have detected an eclipsing signal with a period of about 465 s from this source, and we note that the periodic signal is detected exclusively during the source's high-luminosity states. This signal probably originates from its orbital motion; therefore, it is an ultra-compact X-ray binary (UCXB) candidate with the highest X-ray luminosity. Our theoretical analyses show that M31 UCXB-1 is in good agreement with the luminosity-orbital period relation (L 2-10 keV-P orb) of the black hole/neutron star-white dwarf (BH/NS-WD) UCXB system. Moreover, our spectral analyses indicate that the primary in M31 UCXB-1 is more likely to be a BH than an NS. The results show that M31 UCXB-1 is a BH-WD system, with the shortest orbital period, the possibly strongest gravitational wave emission, and the most massive WD among the known UCXBs.
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