标题： 从NGC 6814中的一个高度信息丰富的X射线掩食事件中能学到什么？ 奇妙的吸收体 显示英文标题

标题： What can be learnt from a highly informative X-ray occultation event in NGC 6814? A marvellous absorber

摘要： 报告了在2016年XMM-Newton观测期间NGC 6814中发生的一次独特的X射线掩食事件，该事件提供了吸收体和冕层的有用信息。 我们借助硬度比（HR）-计数率（CR）图以及与2009年和2021年的两次无吸收的XMM曝光进行比较，重新审视了这一事件。 在曝光过程中，NGC 6814表现出明显的“更亮时更软”变化模式，但在HR-CR图中，2016年的曝光明显偏离了其他两个曝光。 虽然光谱拟合确实产生了与2016年日食事件相对应的瞬态康普顿薄吸收，但修正这种瞬态康普顿薄吸收并没有缓解HR-CR图中的紧张关系，反而在2016年的曝光中导致了新的严重偏离。 我们表明，遮挡吸收体应该是块状的（而不是单一的康普顿薄云），其中内部较密区域由康普顿薄云和康普顿厚云组成，负责之前识别出的掩食事件，而外部较稀疏区域则由康普顿薄云组成，这些云遮挡了整个2016年的曝光。 通过这个模型，在HR-CR图中的所有紧张关系都可以自然消除，2016年曝光期间观察到的光谱变化主要由吸收的变化主导。 此外，2016年曝光中检测到的两个温吸收体（具有不同的电离度和柱密度，但相似的流出速度）也应与瞬态吸收体相关联，可能是由于被剥离或潮汐拉伸/破坏的碎片。 这项工作强调了HR-CR图在分析罕见掩食事件时的独特用途。 显示英文摘要

摘要： A unique X-ray occultation event in NGC 6814 during an XMM-Newton observation in 2016 has been reported, providing useful information of the absorber and the corona. We revisit the event with the aid of the hardness ratio (HR) - count rate (CR) plot and comparison with two other absorption-free XMM exposures in 2009 and 2021. NGC 6814 exhibits a clear "softer-when-brighter" variation pattern during the exposures, but the 2016 exposure significantly deviates from the other two in the HR - CR plot. While spectral fitting does yield transient Compton-thin absorption corresponding to the eclipse event in 2016, rather than easing the tension between exposures in the HR - CR plot, correcting the transient Compton-thin absorption results in new and severe deviation within the 2016 exposure. We show that the eclipsing absorber shall be clumpy (instead of a single Compton-thin cloud), with an inner denser region composed of both Compton-thin and Compton-thick clouds responsible for the previously identified occultation event, and an outer sparser region with Compton-thin clouds which eclipses the whole 2016 exposure. With this model, all the tension in the HR - CR plots could be naturally erased, with the observed spectral variability during the 2016 exposure dominated by the variation of absorption. Furthermore, the two warm absorbers (with different ionization and column densities but similar outflowing velocities) detected in the 2016 exposure shall also associate with the transient absorber, likely due to ablated or tidal stretched/disrupted fragments. This work highlights the unique usefulness of the HR - CR plot while analysing rare occultation events.