AT 2021loi photometry & sp. follow-up

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 1yr after the main peak (which was not explicitly identified but might be the case in all previous BFFs). An emission feature around 4680{AA}, 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 NIII{lambda}4640 with HeII{lambda}4686 as its origin.