四个“高变”AGN的光谱分析：大海捞针？
Spectral analysis of four 'hypervariable' AGN: a microneedle in the haystack?
摘要：
我们分析了四个极端的活动星系核（AGN）瞬变，以探讨它们是由罕见的，高振幅的微透镜事件引起的可能性。这些以前未知的Ⅰ型活动星系核位于红移0.6-1.1的范围内，在~年的时间尺度上，g带的变化大于1.5等。来自威廉·赫歇尔望远镜的多历元光谱学显示了宽谱线通量相对于连续谱线变化和谱线轮廓演变的明显差异变化。在两种情况下，一个简单的点源，点透镜微透镜模型提供了一个很好的匹配，在这些对象中看到的长期变化。对于这两个模型，参数约束是一致的微透镜是由于干预恒星质量的对象，但尚未有一个干预星系的存在确认。模型预测的峰值放大率为10.3/13.5和爱因斯坦时间尺度为7.5/10.8年，分别。在一种情况下，数据还允许对CIII]发射区域的大小的限制，在一些简化的假设下，为约1.0-6.5光日，并且对Mg II发射区域的大小的下限为> 9光日（半光半径）。这个CIII]半径可能是令人惊讶的小。在剩下的两个物体中，有光谱学证据表明有一个介入的吸收体，但是在光变曲线中看到的额外结构需要一个更复杂的透镜场景来充分解释。
英文摘要：
We analyze four extreme active galactic nuclei (AGN) transients to explore the possibility that they are caused by rare, high-amplitude microlensing events. These previously unknown type-I AGN are located in the redshift range 0.6-1.1 and show changes of > 1.5 mag in the g-band on a time-scale of ~years. Multi-epoch optical spectroscopy, from the William Herschel Telescope, shows clear differential variability in the broad line fluxes with respect to the continuum changes and also evolution in the line profiles. In two cases, a simple point-source, point-lens microlensing model provides an excellent match to the long-term variability seen in these objects. For both models, the parameter constraints are consistent with the microlensing being due to an intervening stellar mass object but as yet there is no confirmation of the presence of an intervening galaxy. The models predict a peak amplification of 10.3/13.5 and an Einstein time-scale of 7.5/10.8 yr, respectively. In one case, the data also allow constraints on the size of the CIII] emitting region, with some simplifying assumptions, to to be ~1.0-6.5 light-days and a lower limit on the size of the MgII emitting region to be > 9 light-days (half-light radii). This CIII] radius is perhaps surprisingly small. In the remaining two objects, there is spectroscopic evidence for an intervening absorber but the extra structure seen in the light curves requires a more complex lensing scenario to adequately explain.
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