AT 2021loi: A Bowen Fluorescence Flare with a Rebrightening Episode Occurring in a Previously Known AGN

Lydia Makrygianni*, Benny Trakhtenbrot, Iair Arcavi, Claudio Ricci, Marco C. Lam, Assaf Horesh, Itai Sfaradi, K. Azalee Bostroem, Griffin Hosseinzadeh, D. Andrew Howell, Craig Pellegrino, Rob Fender, David A. Green, David R.A. Williams, Joe Bright

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The optical-ultraviolet transient AT 2021loi is located at the center of its host galaxy. Its spectral features identify it as a member of the Bowen fluorescence flare (BFF) class. The first member of this class was considered to be related to a tidal disruption event, but enhanced accretion onto an already active supermassive black hole was suggested as an alternative explanation. Having occurred in a previously known unobscured active galactic nucleus, AT 2021loi strengthens the latter interpretation. Its light curve is similar to those of previous BFFs, showing a rebrightening approximately 1 yr after the main peak (which was not explicitly identified but might be the case in all previous BFFs). An emission feature around 4680 Å, seen in the preflare spectrum, strengthens by a factor of ∼2 around the optical peak of the flare and is clearly seen as a double-peaked feature then, suggesting a blend of N iii λ4640 with He ii λ4686 as its origin. The appearance of O iii λ3133 and possible N iii λλ4097, 4103 (blended with Hδ) during the flare further support a Bowen fluorescence classification. Here we present ZTF, ATLAS, Keck, Las Cumbres Observatory, NEOWISE-R, Swift AMI, and Very Large Array observations of AT 2021loi, making it one of the best-observed BFFs to date. It thus provides some clarity on the nature of BFFs but also further demonstrates the diversity of nuclear transients.

Original languageAmerican English
Article number32
JournalAstrophysical Journal
Issue number1
StatePublished - 1 Aug 2023

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© 2023. The Author(s). Published by the American Astronomical Society.


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