标题： 脉动超亮X射线源M51 ULX-7中的可能周期性暗淡现象 显示英文标题

标题： Possible Periodic Dips in the Pulsating Ultraluminous X-ray Source M51 ULX-7

摘要： 我们报告了在脉动超亮X射线源M51 ULX-7中发现可能的周期性X射线暗淡现象，这是通过档案中的Chandra观测数据发现的。 在超轨道下降状态下进行约20天的监测，我们通过贝叶斯块技术发现了三个暗淡现象，间隔约为2天和8天。 相位分散最小化和$\chi^2$检验表明，暗淡现象可能以约2天的周期重复出现，这与M51 ULX-7的轨道周期一致。 我们将暗淡现象解释为脉冲星辐射被流-盘相互作用区域的垂直结构或伴星大气所遮挡。 这两种解释都表明观测角度约为60度。 考虑到M51 ULX-7的磁场中等偏高，$B\sim10^{13}$G，低几何束流与$b\lesssim1/2$相结合足以解释观测到的流量和暗淡现象的存在。 恒星风的遮挡仍然是一个可能的替代起源，需要进一步监测暗淡现象。 显示英文摘要

摘要： We report the discovery of possible periodic X-ray dips in a pulsating ultraluminous X-ray source, M51 ULX-7, with the archival Changra observations. With ~20 days of monitoring in the superorbital descending state, we discovered three dips with separations of ~2 and ~8 days via the Bayesian block technique. A phase-dispersion minimization and a $\chi^2$ test suggest that the dip is likely recurrent with a period of ~2 days, consistent with the orbital period of M51 ULX-7. We interpret the dip as an obscuring of the emission from the pulsar by the vertical structure on the stream-disk interaction region or the atmosphere of the companion star. Both interpretations suggest the viewing angle to be ~60 degrees. Given that the magnetic field of M51 ULX-7 is moderately high, $B\sim10^{13}$ G, low geometric beaming with $b\lesssim1/2$ is sufficient to explain the observed flux and the presence of dips. Obscuration of the stellar wind remains an alternative possible origin and further monitoring of the dips will be required.