Hung, T. and Cenko, S. B. and Roth, Nathaniel and Gezari, S. and Veilleux, S. and van Velzen, Sjoert and Gaskell, C. Martin and Foley, Ryan J. and Blagorodnova, N. and Yan, Lin and Graham, M. J. and Brown, J. S. and Siebert, M. R. and Frederick, Sara and Ward, Charlotte and Gatkine, Pradip and Gal-Yam, Avishay and Yang, Yi and Schulze, Steve and Dimitriadis, G. and Kupfer, Thomas and Shupe, David L. and Rusholme, Ben and Masci, Frank J. and Riddle, Reed and Soumagnac, Maayane T. and van Roestel, J. and Dekany, Richard (2019) Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event. The Astrophysical Journal, 879 (2): 119. ISSN 0004-637X
Full text not available from this repository.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.