J/A+A/706/A324 AT2019aalc as a TDE in an AGN (Veres+, 2026)
Back from the dead: AT2019aalc as a candidate repeating tidal disruption event
in an active galactic nucleus.
Veres P.M., Franckowiak A., van Velzen S., Adebahr B., Taziaux S.,
Necker J., Stein R., Kier A., Mueller A., Bomans D.J., Jordana-Mitjans N.,
Kowalski M., Hammerstein E., Marci-Boehncke E., Reusch S., Garrappa S.,
Rose S., Kashyap Das K.
<Astron. Astrophys. 706, A324 (2026)>
=2026A&A...706A.324V 2026A&A...706A.324V (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; X-ray sources ; Galaxies, spectra ;
Galaxies, Seyfert
Keywords: neutrinos - galaxies: active - galaxies: individual: AT2019aalc -
quasars: emission lines - galaxies: Seyfert -
radio continuum: galaxies
Abstract:
To date, three nuclear transients have been associated with
high-energy neutrino events. These transients are generally
thought to be powered by tidal disruptions of stars (TDEs) by massive
black holes. However, AT2019aalc, hosted in a Seyfert-1 galaxy, was
not yet classified due to a lack of multiwavelength observations.
Interestingly, the source has re-brightened 4 years after its
discovery.To date, three nuclear transients have been associated with
high-energy neutrino events. These transients are generally thought to
be powered by tidal disruptions of stars (TDEs) by massive black
holes. However, AT2019aalc, hosted in a Seyfert-1 galaxy, was not yet
classified due to a lack of multiwavelength observations.
Interestingly, the source has re-brightened 4 years after its
discovery.
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.
We conducted a multi-wavelength monitoring program (from radio to
X-rays) of AT2019aalc during its re-brightening in 2023/2024.
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, similarly to the first one, is also
accompanied by IR dust echo emission. A long-term radio flare is found
with an inverted spectrum. Optical spectroscopic observations reveal
the presence of Bowen Fluorescence lines and strong high-ionization
coronal lines indicating an extreme level of ionization in the system.
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 (AGN). AT2019aalc can be also classified as an extreme
coronal line emitter (ECLE). We found 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 multi-wavelength properties of AT2019aalc and
suggest a possible connection among ECLEs, BFFs, and TDEs occurring in
AGNs.
Description:
We present reduced optical spectroscopic data of the nuclear transient
AT2019aalc (ZTF19aaejtoy) which occurred in the Seyfert-1 galaxy
Z 49-155 (z=0.03557). The initial optical flare occurred in 2019,
followed by a second flare four years later. Based on multi-wavelength
observations, the transient was classified as a Bowen fluorescence
flare.
We tabulate data of five reduced optical spectra of AT2019aalc
observed with the Low Resolution Imaging Spectrograph (LRIS: Oke et
al., 1995PASP..107..375O 1995PASP..107..375O) mounted on the Keck-I telescope at Maunakea
(PI: Kulkarni) and the Double Beam Spectrograph (DBSP, Oke & Gunn
1982PASP...94..586O 1982PASP...94..586O) mounted on the 200 inch telescope at Palomar
Observatory, California (PIs: Kulkarni and Kasliwal). The first LRIS
spectrum was observed between the two optical flares while the other
four spectra during the second flare. The second LRIS spectrum and the
first DBSP spectrum were obtained before the peak of the second flare,
while the second and third DBSP spectra were taken afterward. All
spectra are flux-calibrated and corrected for Galactic extinction.
Wavelengths are in vacuum and not corrected to rest frame.
Objects:
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RA (2000) DE Designation(s)
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15 24 16.67 +04 51 19.0 AT2019aalc = ZTF19aaejtoy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 25 5123 LRIS spectrum from 2021-06-07T10:31:55
table2.dat 25 5092 LRIS spectrum from 2023-06-15T05:49:14.765
table3.dat 25 4916 DBSP spectrum from 2023-07-11T00:00:00
table4.dat 25 5152 DBSP spectrum from 2023-08-17T03:00:00
table5.dat 25 5230 DBSP spectrum from 2024-05-21T08:49:43
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Byte-by-byte Description of file: table?.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 0.1nm lambda Observed wavelength
15- 25 E11.5 10mW/m2/nm Flux Spectral flux density (in erg/cm2/s/Å)
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Acknowledgements:
Patrik Milan Veres, veres(at)astro.ruhr-uni-bochum.de
(End) Patricia Vannier [CDS] 14-Jan-2026