2026ApJ...997..300H

Active galactic nuclei (AGNs) exhibit variability in their luminosities with timescales that correlate with the mass of the black hole at the centre of the AGN. Presently, the empirical correlation lacks sufficient precision to confidently convert these timescales into black hole masses, especially at the low-mass end. To find more AGNs with timescale measurements, we study a very large catalog of AGNs from Data Release 3 of Gaia, called Gaia variabLE AgN (GLEAN, with 872,228 objects). We identify GLEAN objects with optical spectra from the Sloan Digital Sky Survey Data Release 17 and light curves from the Zwicky Transient Facility (ZTF) Data Release 21. After fitting the light curves with a damped random walk (DRW) model, we find that the GLEAN light curves have insufficient sampling to extract reliable amplitude and timescale measurements outside the range of 50-100 days. On the other hand, well-sampled ZTF light curves allow more accurate estimations of these parameters. The fractional variability amplitude is an effective, model-independent metric for measuring variability amplitude, but only when derived from high-quality light curves. We provide a catalog of 127 GLEAN AGNs with spectroscopic virial black hole masses, and variability amplitudes and timescales. Though we do not find any low-mass black holes in this AGN sample, we confirm a relationship between the DRW timescale and the black hole mass that is consistent with previous studies.