标题： 爱因斯坦探针对EP J182730.0-095633的发现：一个暗弱爆发中的新型黑洞X射线双星候选体？ 显示英文标题

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

摘要： 目前在我们的银河系中被确认的黑洞X射线双星（候选体）主要是暂现源，大多数是通过检测其X射线爆发而发现的。 其中，只有四个是在暗弱爆发中发现的，表现出峰值X射线光度为$L_{\rm X}\lesssim10^{36}~{\rm erg~s^{-1}}$，这可能是由于之前缺乏灵敏的宽视场X射线监测仪器。 在本信中，我们通过爱因斯坦探针（EP）以及随后的多波段后续研究，发现了有趣的X射线暂现源EP J182730.0-095633。 这个暂现源位于银河平面，经历了一个持续约20天的暗弱且短暂的X射线爆发。 其X射线谱是非热的，并与一个近似恒定的光子指数为$\Gamma \sim2$的幂律模型一致。 在其X射线光变曲线中检测到了一个持续时间较长的毫赫兹准周期振荡（QPO）信号，中心频率约为$\sim0.04$Hz。 一个瞬时的近红外源被识别为其对应体，尽管没有检测到光学辐射，这可能是因为显著的消光。 还观测到了一个射电对应体，显示出一个倒置的射电谱，具有$\alpha\sim0.45$。 X射线光谱和时间特征以及多波段特性表明，该源是一个暗弱的低质量X射线双星，致密天体很可能是黑洞。 这项工作展示了EP在捕捉暗弱水平X射线爆发时发现新的X射线双星的潜力。 显示英文摘要

摘要： 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 $L_{\rm X}\lesssim10^{36}~{\rm erg~s^{-1}}$, 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 multi-wavelength 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 non-thermal and consistent with a power-law model with a nearly constant photon index of $\Gamma \sim2$ throughout the outburst. A long-lasting millihertz quasi-periodic oscillation (QPO) signal was detected in its X-ray light curve, centered around a frequency of $\sim0.04$ 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 $\alpha\sim0.45$. The X-ray spectral and temporal characteristics, along with the multi-wavelength 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 capturing faint-level X-ray outbursts.