标题： 位于球状星团 NGC 1851 中的超紧致 X 射线双星 显示英文标题

标题： An ultracompact X-ray binary in the globular cluster NGC 1851

摘要： 我们利用哈勃太空望远镜获得了球状星团NGC 1851中的低质量X射线双星4U 0513-40的远紫外测光数据。 我们的观测揭示了一个清晰的、大致正弦波的周期信号，周期为$P \simeq 17$分钟，振幅为3%-10%。 该信号表现出完全的相干性，并可被建模为与系统中白矮星供体星受辐射面投影面积变化相关的简单再处理效应。 所有这些特性表明，我们所检测到的信号本质上是轨道性的，从而确认4U 0513-40为一个超紧致X射线双星（UCXB）。 所有四个已确认的球状星团中的UCXB都具有低于30分钟的轨道周期，而几乎所有的银河场UCXB都具有更长的轨道周期。 这表明，在星团中动力学形成过程主导了UCXB的产生，导致了与场UCXB不同的轨道周期分布。 基于可能的系统参数，我们显示4U 0513-40应是一个强烈的引力波源，并可能在多年任务期间被LISA探测到。 显示英文摘要

摘要： We present far-ultraviolet photometry obtained with the Hubble Space Telescope of the low-mass X-ray binary 4U 0513-40 in the globular cluster NGC 1851. Our observations reveal a clear, roughly sinusoidal periodic signal with $P \simeq 17$ min and amplitude 3%-10%. The signal appears fully coherent and can be modelled as a simple reprocessing effect associated with the changing projected area presented by the irradiated face of a white dwarf donor star in the system. All of these properties suggest that the signal we have detected is orbital in nature, thus confirming 4U 0513-40 as an ultracompact X-ray binary (UCXB). All four confirmed UCXBs in globular clusters have orbital periods below 30 minutes, whereas almost all UCXBs in the Galactic field have orbital periods longer than this. This suggests that the dynamical formation processes dominate UCXB production in clusters, producing a different orbital period distribution than observed among field UCXBs. Based on the likely system parameters, we show that 4U 0513-40 should be a strong gravitational wave source and may be detectable by LISA over the course of a multi-year mission.