Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548-猫眼课题宝

DOI：

10.3847/1538-4357/ab1b48

发表时间：

2018-12

期刊：

The Astrophysical Journal

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

M. Dehghanian;G. Ferland;G. Kriss;B. Peterson;S. Mathur;M. Mehdipour;F. Guzmán;M. Chatzikos;P. V. Hoof;R. Williams;N. Arav;A. Barth;M. Bentz;S. Bisogni;W. Brandt;D. Crenshaw;E. Bontà;G. D. Rosa;M. Fausnaugh;J. Gelbord;M. Goad;A. Gupta;K. Horne;J. Kaastra;C. Knigge;K. Korista;I. McHardy;R. Pogge;D. Starkey;M. Vestergaard

2014年在NGC 5548上的空间望远镜和光学混响测绘项目(AGN STORM)是有史以来最密集的多波长AGN监测活动之一。在竞选活动的大部分时间里，正如预期的那样，发射线的变化跟随着连续统的变化，并有一段时间滞后。然而，在60-70天的“假期”期间，这些谱线的变化与观测到的紫外光连续谱无关，这表明电离连续谱存在着未被观测到的变化。为了理解这一显著的现象并获得对电离连续谱变化的独立评估，我们研究了NGC5548中存在的本征吸收线。我们确定了一个新的周期，它再现了吸收线的可变性，从而确定了允许假期发生的物理因素。在这个循环中，遮光器视线覆盖系数的变化改变了软X射线连续谱，改变了氦的电离。再结合氦产生的电离辐射会影响哈勃太空望远镜所看到的某些离子的电离水平。特别是，高电离物种受到较模糊覆盖因子变化的影响，这不会影响光学或UV连续谱，因此看起来像是不相关的变化，是一个“假日”。很可能，任何其他在节日期间选择性地改变连续谱软X射线部分的模型也可以解释观察到的异常发射线行为。

The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60–70 day “holiday,” suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer’s line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a “holiday.” It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.

Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548

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