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Extreme variability in an active galactic nucleus: Gaia16aax

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journal contribution
posted on 06.04.2020, 15:32 by G Cannizzaro, M Fraser, PG Jonker, JE Pringle, S Mattila, PC Hewett, T Wevers, E Kankare, Z Kostrzewa-Rutkowska, L Wyrzykowski, F Onori, J Harmanen, KES Ford, B McKernan, CJ Nixon
We present the results of a multiwavelength follow-up campaign for the luminous nuclear transient Gaia16aax, which was first identified in 2016 January. The transient is spatially consistent with the nucleus of an active galaxy at z = 0.25, hosting a black hole of mass ∼6 × 10^8 M. The nucleus brightened by more than 1 mag in the Gaia G band over a timescale of less than 1 yr, before fading back to its pre-outburst state over the following 3 yr. The optical spectra of the source show broad Balmer lines similar to the ones present in a preoutburst spectrum. During the outburst, the H α and H β emission lines develop a secondary peak. We also report on the discovery of two transients with similar light-curve evolution and spectra: Gaia16aka and Gaia16ajq. We consider possible scenarios to explain the observed outbursts. We exclude that the transient event could be caused by a microlensing event, variable dust absorption or a tidal encounter between a neutron star and a stellar mass black hole in the accretion disc. We consider variability in the accretion flow in the inner part of the disc, or a tidal disruption event of a star ≥1 M by a rapidly spinning supermassive black hole as the most plausible scenarios. We note that the similarity between the light curves of the three Gaia transients may be a function of the Gaia alerts selection criteria.

Funding

GC, PGJ, and ZKR acknowledge support from European Research Council Consolidator Grant 647208. MF is supported by a Royal Society – Science Foundation Ireland University Research Fellowship. FO acknowledges the support of the H2020 European Hemera programme, grant agreement no. 730970. JH acknowledges financial support from the Finnish Cultural Foundation and the Vilho, Yrjo and Kalle V ¨ ais ¨ al¨ a Foundation (of the Finnish Academy ¨ of Science and Letters). BM and KESF are supported by National Science Foundation grant 1831412. CJN is supported by the Science and Technology Facilities Council (STFC) (grant numberST/M005917/1).

History

Citation

Monthly Notices of the Royal Astronomical Society, Volume 493, Issue 1, March 2020, Pages 477–495

Version

VoR (Version of Record)

Published in

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Volume

493

Issue

1

Pagination

477 - 495 (19)

Publisher

OXFORD UNIV PRESS

issn

0035-8711

eissn

1365-2966

Acceptance date

10/01/2020

Copyright date

2020

Available date

23/01/2020

Publisher version

https://academic.oup.com/mnras/article-abstract/493/1/477/5714763

Language

English

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