标题： 利用Swift观测的活动星系核X射线掩食事件的系统性搜索 显示英文标题

标题： A Systematic Search for X-ray Eclipse Events in Active Galactic Nuclei Observed by Swift

摘要： 活动星系核（AGN）的核区可能存在着团块状云，这些云偶尔会遮蔽其中心的X射线源，导致掩食事件的发生。 这些事件为研究此类云的性质和起源提供了独特的机会。 然而，由于需要多年的长期X射线监测，这类瞬变事件很少被报道。 在这里，我们对过去20年通过Swift X射线望远镜（XRT）对40个AGN进行了系统的掩食事件搜索，总计包含$\sim$11,000次观测。 我们的选择标准基于X射线流量和光谱形状的显著变化。 我们在3个AGN中识别出3个高置信度事件，在6个AGN中识别出8个候选事件，所有这些都发生在I型AGN中。 观测到的云的柱密度为 $N_{\rm H}~\sim$ (0.2 $-$ 31.2) $\times$ 10$^{22}$ cm$^{-2}$，电离度为 log $\xi$ $\sim$ (-1.3 $-$ 2.2)。 对于这5个持续时间约束良好的事件，它们距离中心黑洞的距离范围为（2.4 $-$ 179） $\times$ 10$^{4}$ $R_{\rm g}$ ，其中有2个云团靠近尘埃亚消光区，另外2个位于更外侧。有趣的是，我们发现云团属性（即电离状态和柱密度）与黑洞质量和吸积率之间存在初步的相关性，这表明它们可能通过外流与吸积过程有很强的联系。我们的研究还展示了新的X射线全天天文监测器爱因斯坦探针（Einstein Probe）在这类事件的探测和物理限制方面所具有的潜力。 显示英文摘要

摘要： The nuclear regions of active galactic nuclei (AGNs) likely host clumpy clouds that occasionally obscure the central X-ray source, causing eclipse events. These events offer a unique opportunity to study the properties and origins of such clouds. However, these transient events are rarely reported due to the need for extensive, long-term X-ray monitoring for years. Here, we conduct a systematic search for eclipse events in 40 AGNs well-monitored by the Swift X-ray Telescope (XRT) over the past 20 years, comprising a total of $\sim$11,000 observations. Our selection criteria rely on significant variations in X-ray flux and spectral shape. We identify 3 high-confidence events in 3 AGNs and 8 candidates in 6 AGNs, all in type I AGNs. The observed clouds have column densities of $N_{\rm H}~\sim$ (0.2 $-$ 31.2) $\times$ 10$^{22}$ cm$^{-2}$ and ionization degrees of log $\xi$ $\sim$ (-1.3 $-$ 2.2). For the 5 events with well-constrained duration, their distances from the central black hole range from (2.4 $-$ 179) $\times$ 10$^{4}$ $R_{\rm g}$, with 2 clouds near the dust sublimation zone, 2 farther out. Interestingly, we find tentative correlations between the cloud properties (i.e. ionization state and column density) and the black hole mass and mass accretion rate, implying their strong connection to the accretion process, potentially via outflows. Our study also demonstrates the potential of the new X-ray all-sky monitor, Einstein Probe, in providing more detection and physical constraints for such events.