The first extragalactic ultra-compact X-ray binary : a candidate black hole-white dwarf system
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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866909939979517952 |
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| author | Ma, Qian-Qi Zhang, Jiachang Gu, Wei-Min Li, Zhiyuan Weng, Shan-Shan Bao, Tong |
| author_facet | Ma, Qian-Qi Zhang, Jiachang Gu, Wei-Min Li, Zhiyuan Weng, Shan-Shan Bao, Tong |
| contents | M31 UCXB-1 is one of the brightest X-ray point sources in the bulge of M31, with a peak X-ray luminosity $ L_{\mathrm{0.5-10 \: keV}} = 2.9^{+0.2}_{-0.2} \times 10^{38} \: \mathrm{erg} \: \mathrm{s}^{-1} $. Both XMM-Newton and Chandra observations have detected an eclipsing signal with a period of about 465 seconds from this source, and we note that the periodic signal is detected exclusively during the source's high-luminosity states. This signal probably originates from its orbital motion, therefore it is an ultra-compact X-ray binary (UCXB) candidate with the highest X-ray luminosity. Our theoretical analyses show that M31 UCXB-1 is in good agreement with the luminosity-orbital period relation ($ L_{\mathrm{2-10 \: keV}}-P_{\mathrm{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 rather 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 white dwarf among the known UCXBs. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_02360 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The first extragalactic ultra-compact X-ray binary : a candidate black hole-white dwarf system Ma, Qian-Qi Zhang, Jiachang Gu, Wei-Min Li, Zhiyuan Weng, Shan-Shan Bao, Tong High Energy Astrophysical Phenomena Solar and Stellar Astrophysics M31 UCXB-1 is one of the brightest X-ray point sources in the bulge of M31, with a peak X-ray luminosity $ L_{\mathrm{0.5-10 \: keV}} = 2.9^{+0.2}_{-0.2} \times 10^{38} \: \mathrm{erg} \: \mathrm{s}^{-1} $. Both XMM-Newton and Chandra observations have detected an eclipsing signal with a period of about 465 seconds from this source, and we note that the periodic signal is detected exclusively during the source's high-luminosity states. This signal probably originates from its orbital motion, therefore it is an ultra-compact X-ray binary (UCXB) candidate with the highest X-ray luminosity. Our theoretical analyses show that M31 UCXB-1 is in good agreement with the luminosity-orbital period relation ($ L_{\mathrm{2-10 \: keV}}-P_{\mathrm{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 rather 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 white dwarf among the known UCXBs. |
| title | The first extragalactic ultra-compact X-ray binary : a candidate black hole-white dwarf system |
| topic | High Energy Astrophysical Phenomena Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2512.02360 |