树枝上的变色龙：NGC 247 ULX-1中的光谱态跃迁和下降
The chameleon on the branches: spectral state transition and dips in NGC 247 ULX-1
摘要：
软超亮X射线（ULX）源是ULX的一个子类，可以从超软光谱状态（其中大部分亮度在1 keV以下发射）切换到软光谱状态（其中大部分亮度在1 keV以上发射）。在一些系统中，已经观察到下降。这种状态转换背后的机制和下降的性质仍然存在争议。为了调查这些问题，我们获得了这类成员NGC 247 ULX-1的长XMM-牛顿监测活动。我们计算了整个数据集的硬度-强度图，并确定了两个不同的分支：正常分支和倾斜分支，我们分别用四个和三个硬度-强度分辨光谱进行研究。所有七个光谱都很好地描述了两个热分量：一个较冷的（$kT_{\rm bb}$ $\sim$ 0.1-0.2 keV）黑体，解释为从光球的辐射驱动风的发射，和一个较热的（$kT_{\rm disk}$ $\sim$ 0.6 keV）多色磁盘黑体，可能是由于再处理的辐射从最里面的区域发出。此外，一个复杂的模式的发射和吸收线已被考虑到基于以前的高分辨率光谱结果。我们研究了两个分支的光谱参数和两个热分量的通量的演化，并讨论了两种可能的情况下连接的状态转换和浸渍现象。一种是基于几何掩星的发射区，其他调用的螺旋桨效应的发病。
英文摘要：
Soft Ultra-Luminous X-ray (ULXs) sources are a subclass of the ULXs that can switch from a supersoft spectral state, where most of the luminosity is emitted below 1 keV, to a soft spectral state with significant emission above 1 keV. In a few systems, dips have been observed. The mechanism behind this state transition and the dips nature are still debated. To investigate these issues, we obtained a long XMM-Newton monitoring campaign of a member of this class, NGC 247 ULX-1. We computed the hardness-intensity diagram for the whole dataset and identified two different branches: the normal branch and the dipping branch, which we study with four and three hardness-intensity resolved spectra, respectively. All seven spectra are well described by two thermal components: a colder ($kT_{\rm bb}$ $\sim$ 0.1-0.2 keV) black-body, interpreted as emission from the photo-sphere of a radiatively-driven wind, and a hotter ($kT_{\rm disk}$ $\sim$ 0.6 keV) multicolour disk black-body, likely due to reprocessing of radiation emitted from the innermost regions. In addition, a complex pattern of emission and absorption lines has been taken into account based on previous high-resolution spectroscopic results. We studied the evolution of spectral parameters and the flux of the two thermal components along the two branches and discuss two scenarios possibly connecting the state transition and the dipping phenomenon. One is based on geometrical occultation of the emitting regions, the other invokes the onset of a propeller effect.
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