Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event

T. Hung, S. B. Cenko, Nathaniel Roth, S. Gezari, S. Veilleux, Sjoert Van Velzen, C. Martin Gaskell, Ryan J. Foley, N. Blagorodnova, Lin Yan, M. J. Graham, J. S. Brown, M. R. Siebert, Sara Frederick, Charlotte Ward, Pradip Gatkine, Avishay Gal-Yam, Yi Yang, S. Schulze, G. DimitriadisThomas Kupfer, David L. Shupe, Ben Rusholme, Frank J. Masci, Reed Riddle, Maayane T. Soumagnac, J. Van Roestel, Richard Dekany

Research output: Contribution to journalArticlepeer-review

36 Scopus citations

Abstract

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.

Original languageEnglish
Article number119
JournalAstrophysical Journal
Volume879
Issue number2
DOIs
StatePublished - 10 Jul 2019
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved..

Keywords

  • accretion, accretion disks
  • black hole physics
  • galaxies: nuclei
  • ultraviolet: general

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