Kavli Affiliate: Claudio Ricci
| First 5 Authors: Marzena Śniegowska, Benny Trakhtenbrot, Lydia Makrygianni, Iair Arcavi, Claudio Ricci
| Summary:
AT 2019aalc is a peculiar sequence of highly variable emission events
observed towards the nucleus of the broad-line AGN SDSS J152416.66+045119.0.
The system exhibited two distinct UV/optical flares (the first detected in
2019, the second one in 2023). Spectra obtained following the detection of the
second flare revealed prominent Bowen fluorescence and high-ionization coronal
emission lines, which were much weaker, if at all detectable, in a spectrum
taken following the first flare. We present and analyze a large set of
multi-wavelength, multi-epoch data for this source, with particular emphasis on
optical spectroscopic monitoring conducted with the Las Cumbres Observatory
network. During the relatively slow dimming that followed the second optical
flare, the UV/optical light-curve shows a sequence of minor rebrightening
events, while the Bowen fluorescence and the coronal lines vary (roughly) in
tandem with these "bumps" in the broad-band light-curve. Most of the observed
behavior of AT 2019aalc links it to the growing class of Bowen fluorescence
flares (BFFs) while setting it apart from canonical tidal disruption events.
However, AT 2019aalc has some outstanding peculiarities, including two short
flares seen in its soft X-ray light-curve during the dimming phase of the
second optical flare, and which do not seem to be linked to the emission line
variations. We discuss the optical and X-ray properties of the source and
possible scenarios of the origin of the flare, in particular radiation pressure
instabilities in the (pre-existing) AGN accretion disk.
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