AGN in Gaia Alerts: from flares to Changing Look Quasars
M. Dennefeld, T. Pursimo, C. Carvalho, E. Biancalani, M.A. Diaz Teodori, O. Durfeldt Pedros, M.A. Fetzner Keniger, A. Kasikov, N. Koivisto, J. Martikainen, K. Matilainen, J. Sinkbak Thomsen, J. Terwel, A. Viitanen

TL;DR
This paper reports on Gaia Alert detections of variable AGN and quasars, confirming 64 new candidates, analyzing over 200 known AGN, and revealing phenomena like flares, TDEs, and Changing Look Quasars, highlighting variability as a key detection tool.
Contribution
It provides the first spectroscopic confirmation of Gaia-identified variable AGN and quasars, and characterizes the diverse phenomena causing their variability, including a significant fraction of Changing Look Quasars.
Findings
Confirmed 64 new Gaia AGN/quasar candidates.
Identified 56 secure and 23 probable Changing Look Quasars.
Observed diverse phenomena including flares, TDEs, and microlensing events.
Abstract
The Gaia Alerts system is providing alerts on a variety of objects displaying a significant photometric change detected by the Gaia satellite from one passage to the next one over the same region of the sky. Among the over 22000 alerts published until the end of 2022, around 13 percent concern AGN or quasar candidates. We have embarked on a spectroscopic ground-based follow-up of some of those (including some selected by a different method specifically in galactic nuclei), to establish their true nature, and reveal the various phenomena leading to a change in magnitude of those AGN. The present paper deals with radio-quiet objects, while the radio-loud ones will be described in a companion paper. We confirm, on one hand, the AGN/quasar nature of 64 new candidates alerted by Gaia, and, on the other hand, obtained second-epoch spectra of over 200 known AGN also alerted for large…
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Taxonomy
TopicsAstronomy and Astrophysical Research · Gamma-ray bursts and supernovae · Stellar, planetary, and galactic studies
