Journal Article

PUBDB-2026-01179

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Back from the dead: AT2019aalc as a candidate repeating tidal disruption event in an active galactic nucleus

Veres, P. M. (Corresponding author) ; Franckowiak, A.Extern* ; van Velzen, S. ; Adebahr, B. ; Taziaux, S. ; Necker, J.DESY* ; Stein, R. ; Kier, A. ; Müller, A. ; Bomans, D. J. ; Jordana-Mitjans, N. ; Kowalski, M.DESY* ; Hammerstein, E. ; Marci-Boehncke, E. ; Reusch, S.Extern* ; Garrappa, S.Extern* ; Rose, S. ; Das, K. K.

2026
EDP Sciences Les Ulis

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Please use a persistent id in citations: doi:10.1051/0004-6361/202452051

Abstract: Context. To date, three nuclear transients have been associated with high-energy neutrino events. These transients are generally thought to be powered by tidal disruption events (TDEs) in stars caused by massive black holes. However, AT2019aalc, hosted in a Seyfert-1 galaxy, has not yet been classified due to a lack of multiwavelength observations. Interestingly, the source re-brightened 4 years after its discovery.Aims. Our aim is to constrain the physical mechanism responsible for the second optical flare, which may also provide clues to the origin of the initial event.Methods. We conducted a multiwavelength monitoring program (from radio to X-rays) of AT2019aalc during its re-brightening in 2023–2024.Results. The observations revealed multiple X-ray flares during the second optical flaring episode of the transient and a uniquely bright UV counterpart. The second flare, similar to the first one, is accompanied by IR dust echo emission. A long-term radio flare was found with an inverted spectrum. Optical spectroscopic observations revealed the presence of Bowen fluorescence lines and strong high-ionization coronal lines, indicating an extreme level of ionization in the system.Conclusions. The results suggest that the transient can be classified as a Bowen fluorescence flare (BFF), a relatively new sub-class of flaring active galactic nuclei (AGNs). AT2019aalc can be also classified as an extreme coronal line emitter (ECLE). We find that in addition to AT2019aalc, another BFF, AT2021loi, is spatially coincident with a high-energy neutrino event. We propose a repeating TDE scenario within an AGN framework to explain the multiwavelength properties of AT2019aalc and suggest a possible connection among ECLEs, BFFs, and TDEs occurring in AGNs.

Note: cc-by

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Contributing Institute(s):

1. Neutrinoastronomie / Kosmologie (Z_NA)
2. IceCube+NG (Z_ICE)

Research Program(s):

1. SFB 1491 F07 - Skalenübergreifende Plasmadynamik für die Untersuchung relativistischer kosmischer Jets (F07#) (530489667) (530489667)
2. 613 - Matter and Radiation from the Universe (POF4-613) (POF4-613)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2026

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF >= 5 ; JCR ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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