A new class of flares from accreting supermassive black holes

Benny Trakhtenbrot*, Iair Arcavi, Claudio Ricci, Sandro Tacchella, Daniel Stern, Hagai Netzer, Peter G. Jonker, Assaf Horesh, Julián Esteban Mejía-Restrepo, Griffin Hosseinzadeh, Valentina Hallefors, D. Andrew Howell, Curtis McCully, Mislav Baloković, Marianne Heida, Nikita Kamraj, George Benjamin Lansbury, Łukasz Wyrzykowski, Mariusz Gromadzki, Aleksandra HamanowiczS. Bradley Cenko, David J. Sand, Eric Y. Hsiao, Mark M. Phillips, Tiara R. Diamond, Erin Kara, Keith C. Gendreau, Zaven Arzoumanian, Ron Remillard

*Corresponding author for this work

Research output: Contribution to journalLetterpeer-review

62 Scopus citations


Accreting supermassive black holes (SMBHs) can exhibit variable emission across the electromagnetic spectrum and over a broad range of timescales. The variability of active galactic nuclei (AGNs) in the ultraviolet and optical is usually at the few tens of per cent level over timescales of hours to weeks 1 . Recently, rare, more dramatic changes to the emission from accreting SMBHs have been observed, including tidal disruption events 2–5 , ‘changing look’ AGNs 6–9 and other extreme variability objects 10,11 . The physics behind the ‘re-ignition’, enhancement and ‘shut-down’ of accretion onto SMBHs is not entirely understood. Here we present a rapid increase in ultraviolet–optical emission in the centre of a nearby galaxy, marking the onset of sudden increased accretion onto a SMBH. The optical spectrum of this flare, dubbed AT 2017bgt, exhibits a mix of emission features. Some are typical of luminous, unobscured AGNs, but others are likely driven by Bowen fluorescence—robustly linked here with high-velocity gas in the vicinity of the accreting SMBH. The spectral features and increased ultraviolet flux show little evolution over a period of at least 14 months. This disfavours the tidal disruption of a star as their origin, and instead suggests a longer-term event of intensified accretion. Together with two other recently reported events with similar properties, we define a new class of SMBH-related flares. This has important implications for the classification of different types of enhanced accretion onto SMBHs.

Original languageAmerican English
Pages (from-to)242-250
Number of pages9
JournalNature Astronomy
Issue number3
StatePublished - 1 Mar 2019

Bibliographical note

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© 2019, The Author(s), under exclusive licence to Springer Nature Limited.


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