Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event
Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event
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DOI：
10.3847/1538-4357/ab24de
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发表时间：
2019-03
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通讯作者：
T. Hung;S. Cenko;S. B. Cenko;Nathaniel Roth;S. Gezari;S. Veilleux;S. Velzen;S. Velzen;C. Gaskell;R. Foley;N. Blagorodnova;Lin Yan;M. Graham;J. Brown;M. Siebert;S. Frederick;C. Ward;P. Gatkine;A. Gal-yam;Yi Yang;S. Schulze;G. Dimitriadis;T. Kupfer;D. Shupe;B. Rusholme;F. Masci;R. Riddle;M. Soumagnac;J. Roestel;R. Dekany
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作者：
T. Hung;S. Cenko;S. B. Cenko;Nathaniel Roth;S. Gezari;S. Veilleux;S. Velzen;S. Velzen;C. Gaskell;R. Foley;N. Blagorodnova;Lin Yan;M. Graham;J. Brown;M. Siebert;S. Frederick;C. Ward;P. Gatkine;A. Gal-yam;Yi Yang;S. Schulze;G. Dimitriadis;T. Kupfer;D. Shupe;B. Rusholme;F. Masci;R. Riddle;M. Soumagnac;J. Roestel;R. Dekany
我们报告了在潮汐破裂事件（TDE）AT2018zr（z = 0.071）的光谱中发现的非恒星氢Balmer和亚稳态氦吸收线，伴随着一个瞬态的高速（0.05c）宽吸收线（BAL）系统。在哈勃太空望远镜的紫外光谱中，高电离线和低电离线的吸收也存在于这个速度，使AT2018zr类似于低电离BALQSO。我们的结论是，这些瞬态吸收功能更有可能出现在快速流出产生的TDE比吸收的未结合的碎片。根据流出图象，我们能够再现球形膨胀介质中的平顶Hα发射，而不需要调用椭圆盘的典型规定。我们还报告了在AT 2018 zr的后期光谱中出现了窄的（约1000 kms−1）N iii λ4640、He ii λ4686、Hα和Hβ发射，这可能是斯威夫特观察到的后期紫外连续硬化的结果。包括AT2018zr，我们发现巴尔斯在TDE的UV光谱中具有高缔合率（四分之三）。这表明，外流可能是无处不在的TDEs和不太敏感的视角效应相比，类星体外流。
We report the discovery of nonstellar hydrogen Balmer and metastable helium absorption lines accompanying a transient, high-velocity (0.05c) broad absorption line (BAL) system in the optical spectra of the tidal disruption event (TDE) AT2018zr (z = 0.071). In the Hubble Space Telescope UV spectra, absorption of high- and low-ionization lines is also present at this velocity, making AT2018zr resemble a low-ionization BALQSO. We conclude that these transient absorption features are more likely to arise in fast outflows produced by the TDE than absorbed by the unbound debris. In accordance with the outflow picture, we are able to reproduce the flat-topped Hα emission in a spherically expanding medium without invoking the typical prescription of an elliptical disk. We also report the appearance of narrow (∼1000 kms−1) N iii λ4640, He ii λ4686, Hα, and Hβ emission in the late-time optical spectra of AT2018zr, which may be a result of UV continuum hardening at late times, as observed by Swift. Including AT2018zr, we find a high association rate (three out of four) of BALs in the UV spectra of TDEs. This suggests that outflows may be ubiquitous among TDEs and less sensitive to viewing angle effects compared to QSO outflows.