The tidal disruption event AT 2018hyz - I : double-peaked emission lines and a flat Balmer decrement
Abstract
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 MV ∼ −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 ∼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 (Hα/Hβ ∼ 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.
Citation
Short , P , Nicholl , M , Lawrence , A , Gomez , S , Arcavi , I , Wevers , T , Leloudas , G , Schulze , S , Anderson , J P , Berger , E , Blanchard , P K , Burke , J , Castro Segura , N , Charalampopoulos , P , Chornock , R , Galbany , L , Gromadzki , M , Herzog , L J , Hiramatsu , D , Horne , K , Hosseinzadeh , G , Howell , D A , Ihanec , N , Inserra , C , Kankare , E , Maguire , K , McCully , C , Müller Bravo , T E , Onori , F , Sollerman , J & Young , D R 2020 , ' The tidal disruption event AT 2018hyz - I : double-peaked emission lines and a flat Balmer decrement ' , Monthly Notices of the Royal Astronomical Society , vol. 498 , no. 3 , pp. 4119–4133 . https://doi.org/10.1093/mnras/staa2065
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
ISSN
0035-8711Type
Journal article
Description
Published in MNRAS. Accompanied by companion paper Gomez et al. (2020). Funding: KH acknowledges support from STFC grant ST/R000824/1.Collections
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