1ES 1927+654: An AGN Caught Changing Look on a Timescale of Months
1ES 1927+654: An AGN Caught Changing Look on a Timescale of Months
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DOI：
10.3847/1538-4357/ab39e4
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发表时间：
2019-03
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影响因子：
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通讯作者：
B. Trakhtenbrot;I. Arcavi;C. MacLeod;C. Ricci;E. Kara;M. Graham;D. Stern;F. Harrison;J. Burke-J
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作者：
B. Trakhtenbrot;I. Arcavi;C. MacLeod;C. Ricci;E. Kara;M. Graham;D. Stern;F. Harrison;J. Burke-J
我们研究了1ES 1927+654的突然光学和紫外（UV）增亮，到目前为止，它被称为窄线活动星系核（AGN）。1ES 1927+654是小型且特殊的“真正的2型”活动星系核的一部分，它们缺乏宽的发射线和视线遮蔽。我们的高节奏光谱监测捕捉到了一个蓝色的，无特征的连续体的外观，随后几个星期后出现了广泛的巴耳末发射线。这个时间尺度通常与（持久）宽线活动星系核中中央引擎和宽线发射区之间的预期光旅行时间一致。哈勃太空望远镜光谱学没有显示宽紫外线发射线的证据（例如，C iv λ1549，C iii] λ1909，Mg ii λ2798），可能是由于宽线发射区的尘埃。据我们所知，这是第一个情况下，在连续变化和宽线发射的一个“变化的外观”活动星系核的变化之间的滞后已经在时间上解决。光度和光谱演化的性质和时间尺度不利于视线遮蔽的变化和气体流入的总体速率的变化，因为它们驱动了在AGN中看到的剧烈光谱转换。虽然峰值光度和时间尺度与不活跃星系中的潮汐破裂事件一致，但光谱特性却不一致。X射线发射显示出明显不同的行为，在几小时到几天的时间尺度上频繁发生耀斑，并将在配套出版物中介绍。
We study the sudden optical and ultraviolet (UV) brightening of 1ES 1927+654, which until now was known as a narrow-line active galactic nucleus (AGN). 1ES 1927+654 was part of the small and peculiar class of “true Type-2” AGNs that lack broad emission lines and line-of-sight obscuration. Our high-cadence spectroscopic monitoring captures the appearance of a blue, featureless continuum, followed several weeks later by the appearance of broad Balmer emission lines. This timescale is generally consistent with the expected light travel time between the central engine and the broadline emission region in (persistent) broadline AGN. Hubble Space Telescope spectroscopy reveals no evidence for broad UV emission lines (e.g., C iv λ1549, C iii] λ1909, Mg ii λ2798), probably owing to dust in the broadline emission region. To the best of our knowledge, this is the first case where the lag between the change in continuum and in broadline emission of a “changing look” AGN has been temporally resolved. The nature and timescales of the photometric and spectral evolution disfavor both a change in line-of-sight obscuration and a change of the overall rate of gas inflow as driving the drastic spectral transformations seen in this AGN. Although the peak luminosity and timescales are consistent with those of tidal disruption events seen in inactive galaxies, the spectral properties are not. The X-ray emission displays a markedly different behavior, with frequent flares on timescales of hours to days, and will be presented in a companion publication.