AGN variability in the age of VRO

TL;DR

This paper explores how the Vera C. Rubin Observatory will enable precise measurement of AGN variability parameters, allowing detailed characterization of individual AGN and their population statistics through high-cadence light curve analysis.

Contribution

It demonstrates that VRO will measure AGN variability parameters with unprecedented precision, enabling classification and correlation studies of AGN properties.

Findings

AGN can be separated into ~10 correlation-time-scale bins.

Normalization and power-law index of variability-luminosity relation can be determined to 10^{-4}%.

VRO variability measurements will complement spectroscopy in AGN studies.

Abstract

Over the next ten years, the Vera C.\ Rubin Observatory (VRO) will observe $\sim$10 million active galactic nuclei (AGN) with a regular and high cadence. During this time, the intensities of most of these AGN will fluctuate stochastically. Here, we explore the prospects to quantify precisely these fluctuations with VRO measurements of AGN light curves. To do so, we suppose that each light curve is described by a damped random walk with a given fluctuation amplitude and correlation time. Theoretical arguments and some current measurements suggest that the correlation timescale and fluctuation amplitude for each AGN may be correlated with other observables. We use an expected-information analysis to calculate the precision with which these parameters will be inferred from the measured light curves. We find that the measurements will be so precise as to allow the AGN to be separated into up to $\sim 10$ different correlation-timescale bins. We then show that if the correlation time varies as some power of the luminosity, the normalization and power-law index of that relation will be determined to $\mathcal{O}(10^{-4}\%)$. These results suggest that with VRO, precisely measured variability parameters will take their place alongside spectroscopy in the detailed characterization of individual AGN and in the study of AGN population statistics. Analogous analyses will be enabled by other time-domain projects, such as CMB-S4.