The ‘Big Dipper’: the nature of the extreme variability of the AGN SDSS J2232−0806
The ‘Big Dipper’: the nature of the extreme variability of the AGN SDSS J2232−0806
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DOI：
10.1093/mnras/stz517
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发表时间：
2019-02
影响因子：
4.8
通讯作者：
D. Kynoch;M. Ward;A. Lawrence;A. Bruce;H. Landt;C. MacLeod
中科院分区：
文献类型：
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作者：
D. Kynoch;M. Ward;A. Lawrence;A. Bruce;H. Landt;C. MacLeod
SDSS J2232−0806（“北斗七星”）被认为是一个“慢蓝核超变星”：一个没有已知活动核的星系，蓝色和大幅度的亮度演化发生在几年的时间尺度上。随后的观测表明，这个源确实包含一个活动星系核（AGN）。我们的光学光度和光谱监测活动记录了一个主要的调光事件（和随后的上升）在一段时间内约4年;也有证据表明，以前的事件与此一致的档案数据记录在过去的20年。在这里，我们报告了迄今为止获得的11个光谱的分析，我们组装了一个多波长的数据集，包括红外，紫外和X射线观测。我们发现，一个内在的变化的光度是最有利的解释的意见，基于连续性和线的变化和明显的滞后响应的热尘埃的比较。这个来源，沿着与其他几个最近发现的“改变外观”的对象，表明活动星系核可以表现出大幅度的亮度变化的时间尺度上比标准薄吸积盘模型预测的要短得多。
SDSS J2232−0806 (the ‘Big Dipper’) has been identified as a ‘slow-blue nuclear hypervariable’: a galaxy with no previously known active nucleus, blue colours, and large-amplitude brightness evolution occurring on a time-scale of years. Subsequent observations have shown that this source does indeed contain an active galactic nucleus (AGN). Our optical photometric and spectroscopic monitoring campaign has recorded one major dimming event (and subsequent rise) over a period of around 4 yr; there is also evidence of previous events consistent with this in archival data recorded over the last 20 yr. Here we report an analysis of the 11 optical spectra obtained to date and we assemble a multiwavelength data set including infrared, ultraviolet, and X-ray observations. We find that an intrinsic change in the luminosity is the most favoured explanation of the observations, based on a comparison of continuum and line variability and the apparent lagged response of the hot dust. This source, along with several other recently discovered ‘changing-look’ objects, demonstrate that AGNs can exhibit large-amplitude luminosity changes on time-scales much shorter than those predicted by standard thin accretion disc models.