论文标题
NGC 925 ULX-3的（RE）出现，一种新的瞬态ULX
The (re)appearance of NGC 925 ULX-3, a new transient ULX
论文作者
论文摘要
我们报告了Chandra在2017年11月发现的NGC 925（ULX-3）中发现的第三个ULX，其发光度为$ l _ {\ rm x} =（7.8 \ pm0.8）\ times10^{39} {39} {39} $ erg S $^{ - 1} $^{ - 1} $。 NGC 925的档案数据的检查表明，Swift在2011年以类似高的发光度检测到ULX-3，以及XMM-Newton在2017年1月的同样高亮度，其发光度低得多，$ L _ {\ rm x} =（3.8 \ pm0.5）=（3.8 \ pm0.5）在2005年的其他Chandra未检测的情况下，该对象显示了较高的动态范围> 26。在其高光度检测中，ULX-3表现出具有$γ= 1.6 \ pm0.1 $的硬幂律频谱，而XMM-Newton检测结果稍微柔和，$γ= 1.8^{+0.2} {+0.2} _ { - 0.1} $，并且还具有宽敞的光盘模型。长期的光曲线被稀疏覆盖，并且可以与螺旋桨效应或较大振幅的上浮游时期保持一致，这两种时期都在ULX中看到，尤其是那些具有中子恒星增生器的人。对ULX-3的进一步系统监测将使我们能够确定ULX-3经历其极端变异性并更好地理解ULX的积聚过程的机制。
We report the discovery of a third ULX in NGC 925 (ULX-3), detected in November 2017 by Chandra at a luminosity of $L_{\rm X} = (7.8\pm0.8)\times10^{39}$ erg s$^{-1}$. Examination of archival data for NGC 925 reveals that ULX-3 was detected by Swift at a similarly high luminosity in 2011, as well as by XMM-Newton in January 2017 at a much lower luminosity of $L_{\rm X} = (3.8\pm0.5)\times10^{38}$ erg s$^{-1}$. With an additional Chandra non-detection in 2005, this object demonstrates a high dynamic range of flux of factor >26. In its high-luminosity detections, ULX-3 exhibits a hard power-law spectrum with $Γ=1.6\pm0.1$, whereas the XMM-Newton detection is slightly softer, with $Γ=1.8^{+0.2}_{-0.1}$ and also well-fitted with a broadened disc model. The long-term light curve is sparsely covered and could be consistent either with the propeller effect or with a large-amplitude superorbital period, both of which are seen in ULXs, in particular those with neutron star accretors. Further systematic monitoring of ULX-3 will allow us to determine the mechanism by which ULX-3 undergoes its extreme variability and to better understand the accretion processes of ULXs.
