2015年拱门星系团的NuSTAR和XMM-牛顿观测：来自分子云的衰落硬X射线发射
NuSTAR and XMM-Newton observations of the Arches cluster in 2015: fading hard X-ray emission from the molecular cloud
摘要：
我们目前的结果，长期NuSTAR（200 ks）和XMM牛顿（100 ks）的观测的拱门星团，一个明亮的热源（kT~ 2keV）X射线，具有显著的Fe XXV K_α 6.7keV谱线发射和附近的分子云，其特征在于扩展的非热硬X射线连续谱和荧光Fe K_α 6.4 keV线的中性或低电离态材料周围的集群。分析表明，拱云的非热辐射发生了剧烈的变化，其形态均匀，由荧光Fe K_α线辐射跟踪，在2012年后消失，显示出三个明亮的团块。云排放的下降趋势，如果线性拟合，是一致的半衰期衰减时间约8年。这种强烈的变化已经在银河系中心的其他几个分子云中观察到，包括巨大的分子云Sgr B2，并指向类似的照明锋面传播，推测是由Sgr A* 过去的耀斑活动引起的。
英文摘要：
We present results of long NuSTAR (200 ks) and XMM-Newton (100 ks) observations of the Arches stellar cluster, a source of bright thermal (kT~2 keV) X-rays with prominent Fe XXV K_alpha 6.7 keV line emission and a nearby molecular cloud, characterized by an extended non-thermal hard X-ray continuum and fluorescent Fe K_alpha 6.4 keV line of a neutral or low ionization state material around the cluster. Our analysis demonstrates that the non-thermal emission of the Arches cloud underwent a dramatic change, with its homogeneous morphology, traced by fluorescent Fe K_alpha line emission, vanishing after 2012, revealing three bright clumps. The declining trend of the cloud emission, if linearly fitted, is consistent with half-life decay time of ~8 years. Such strong variations have been observed in several other molecular clouds in the Galactic Centre, including the giant molecular cloud Sgr B2, and point toward a similar propagation of illuminating fronts, presumably induced by the past flaring activity of Sgr A*.
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