论文标题
更换活跃的银河核
Changing-look Active Galactic Nuclei
论文作者
论文摘要
已知活跃的银河核（AGN）在所有可观察到的时间尺度以及整个电磁频谱中显示出通量变化。在过去的十年中，在X射线和光学/UV中，已经观察到越来越多的来源显示出急剧的通量和光谱变化。这些事件通常被描述为“更换AGN”，可以分为两个定义明确的类。更换对象显示出视线柱密度的较强可变性，主要与云或流出的AGN中心发动机相关。更换状态的AGN是对象，其中连续发射和宽发射线出现或消失，通常是由超质量黑洞的积聚速率发生巨大变化而触发的。在这里，我们回顾了我们对这两类更换AGN的当前理解，并讨论开放的问题和未来的前景。
Active Galactic Nuclei (AGN) are known to show flux variability over all observable timescales and across the entire electromagnetic spectrum. Over the past decade, a growing number of sources have been observed to show dramatic flux and spectral changes, both in the X-rays and in the optical/UV. Such events, commonly described as "changing-look AGN", can be divided into two well-defined classes. Changing-obscuration objects show strong variability of the line-of-sight column density, mostly associated with clouds or outflows eclipsing the central engine of the AGN. Changing-state AGN are instead objects in which the continuum emission and broad emission lines appear or disappear, and are typically triggered by strong changes in the accretion rate of the supermassive black hole. Here we review our current understanding of these two classes of changing-look AGN, and discuss open questions and future prospects.
