Einstein Probe Discovery of EP J182730.0−095633: A New Black Hole X-Ray Binary Candidate in Faint Outburst?

作者：Huaqing Cheng, Qingchang Zhao, Lian Tao, Hua Feng, F. Coti Zelati, Haiwu Pan, Ailing Wang, Yanan Wang, M. Y. Ge, A. Rau, A. Marino, Liang Zhang, W. J. Zhang, Francesco Carotenuto, Long Ji, Chichuan Jin, Dongyue Li, B. F. Liu, Yuanqi Liu, Erlin Qiao, N. Rea, Roberto Soria, Song Wang, Zhen Yan, Weimin Yuan, Bing Zhang, Guobao Zhang, Shuang‐Nan Zhang, Weidong Zhang, A. P. Beardmore, Joe Bright, Xinlei Chen, Z. Fan, Shao-Yu Fu, J. P. U. Fynbo, J. Y. Hu, Junjie Jin, P. G. Jonker, A. K. H. Kong, E. Kuulkers, Cheng-Kui Li, Hua-Li Li, Z. K. Lin, Chenxu Liu, He‐Yang Liu, Jinzhong Liu, Xiaowei Liu, Z. Lu, Chandreyee Maitra, Hong-Na Mu, C.‐Y. Ng, Y. L. Qiu, Samaporn Tinyanont, Yun Wang, Wen Shu-Xian, Shanshan Weng, Jianfeng Wu, D. Xu, Y. K. Yan, Zhen Yan, Yuan-Pei Yang, Peng Zhang, Shuang‐Nan Zhang, Qingzhou Zhao, Z. -M. Cai, Yong Chen, Yunfei Chen, Chenzhou Cui, W. W. Cui, H. B. Hu, Ming‐Hsi Huang, S. M. Jia, Ge Jin, Z. X. Ling, Haiqing Liu, S. L. Sun, Xiaofang Sun, Yunfei Xu, Chunhua Zhang, M. Zhang, Y. H. Zhang · 发表于：The Astrophysical Journal Letters · 年份：2025 · DOI：10.3847/2041-8213/adf104 · 被引用次数：5 · 研究领域：Astrophysical Phenomena and Observations、Pulsars and Gravitational Waves Research、Astrophysics and Cosmic Phenomena

Abstract Black hole X-ray binaries (candidates) currently identified in our Galaxy are mainly transient sources, with the majority discovered through the detection of their X-ray outbursts. Among these, only four were found during faint outbursts exhibiting peak X-ray luminosities L X ≲ 10 36 erg s −1 , likely due to the previous lack of sensitive, wide-field monitoring instruments in the X-ray band. In this Letter, we present the discovery of an intriguing X-ray transient, EP J182730.0−095633, via the Einstein Probe (EP) and subsequent multiwavelength follow-up studies. This transient, located on the Galactic plane, experienced a faint and brief X-ray outburst lasting about 20 days. Its X-ray spectrum is nonthermal and consistent with a power-law model with a nearly constant photon index of Γ ∼ 2 throughout the outburst. A long-lasting mHz quasiperiodic oscillation signal was detected in its X-ray light curve, centered around a frequency of ∼0.04 Hz. A transient near-infrared source was identified as its counterpart, although no optical emission was detectable, likely due to significant extinction. A radio counterpart was also observed, displaying an inverted radio spectrum with α ∼ 0.45. The X-ray spectral and temporal characteristics, along with the multiwavelength properties, indicate that the source is a faint low-mass X-ray binary, with the compact object likely being a black hole. This work demonstrates the potential of the EP in discovering new X-ray binaries by captu...