Optical variability of Gaia CRF3 sources with robust statistics and the 5000 most variable quasars

TL;DR

This study analyzes Gaia DR3 light curves for over 11.7 million sources, identifying the most variable quasars and AGNs using robust statistics, revealing their variability characteristics and color-brightness correlations.

Contribution

It introduces a robust statistical approach to characterize variability in Gaia sources and publishes a catalog of the 5000 most variable quasars, highlighting their properties and relation to ICRF3.

Findings

Most CRF sources have moderate variability amplitudes below 0.1 mag.

Variability amplitudes follow a Maxwell-like distribution with a scale of 0.078 mag.

Most quasars become bluer when brighter, with positive correlations in color and magnitude.

Abstract

Using the light curve time series data for more than 11.7 million variable sources published in the Gaia Data Release 3, the average magnitudes, colors, and variability parameters have been computed for 0.836 million Gaia CRF objects, which are mostly quasars and active galactic nuclei (AGNs). To mitigate the effects of occasional flukes in the data, robust statistical measures have been employed, namely, the median, median absolute deviation, and Spearman correlation. We find that the majority of the CRF sources have moderate amplitudes of variability in the Gaia $G$ band just below 0.1 mag. The heavy-tailed distribution of variability amplitudes (quantified as robust standard deviations) does not find a single analytical form, but is closer to Maxwell distribution with a scale of 0.078 mag. The majority of CRF sources have positive correlations between $G$ magnitude and $G_{\rm BP}-G_{\rm RP}$ colors, meaning that these quasars and AGNs become bluer when they are brighter. The variations in the BP and RP bands are also mostly positively correlated. Dependencies of all variability parameters with cosmological redshift are fairly flat for the more accurate estimates above redshift 0.7, while the median color shows strong systematic variations with redshift. Using a robust normalized score of magnitude deviations, a sample of 5000 most variable quasars is selected and published. The intersection of this sample with the ICRF3 catalog shows a much higher rate of strongly variable quasars (mostly, blazars) in ICRF3.