A1 Refereed original research article in a scientific journal
The tidal disruption event AT2018hyz-I. Double-peaked emission lines and a flat Balmer decrement
Authors: P. Short, M. Nicholl, A. Lawrence, S. Gomez, I. Arcavi, T. Wevers , G. Leloudas, S. Schulze, J. P. Anderson, E. Berger, P. K. Blanchard,J. Burke, N. Castro Segura, P. Charalampopoulos, R. Chornock, L. Galbany , M. Gromadzki, L. J. Herzog, D. Hiramatsu, Keith Horne, G. Hosseinzadeh, D. Andrew Howell, N. Ihanec, C. Inserra , E. Kankare, K. Maguire, C. McCully, T. E. M¨uller Bravo , F. Onori , J. Sollerman, D. R. Young
Publisher: OXFORD UNIV PRESS
Publication year: 2020
Journal: Monthly Notices of the Royal Astronomical Society
Journal name in source: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Journal acronym: MON NOT R ASTRON SOC
Volume: 498
Issue: 3
First page : 4119
Last page: 4133
Number of pages: 15
ISSN: 0035-8711
eISSN: 1365-2966
DOI: https://doi.org/10.1093/mnras/staa2065
Self-archived copy’s web address: https://arxiv.org/abs/2003.05470
We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the All-Sky Automated Survey for Supernova survey at an absolute magnitude of M-V similar to -20.2 mag, in the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. High cadence follow-up spectra show broad Balmer lines and He I in early spectra, with He II making an appearance after similar to 70-100 d. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disc emission, and back to smooth at late times. The Balmer lines are unlike typical active galactic nucleus in that they show a flat Balmer decrement (H alpha/H beta similar to 1.5), suggesting the lines are collisionally excited rather than being produced via photoionization. The flat Balmer decrement together with the complex profiles suggests that the emission lines originate in a disc chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material due to a possible partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He II may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.
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