The relation between optical and X-ray variability in Seyfert galaxies

TL;DR

This paper reviews the complex relationship between optical and X-ray variability in Seyfert galaxies, highlighting diverse observational results and discussing potential theoretical explanations involving accretion flow models.

Contribution

It provides a comprehensive review of optical and X-ray variability studies in Seyfert galaxies, emphasizing the observational challenges and theoretical implications.

Findings

Diverse correlations observed between optical and X-ray variability.

Some sources show correlated optical and X-ray flux variations.

Standard models struggle to explain all observed variability patterns.

Abstract

Studying simultaneous optical and X-ray light curves of radio-quiet AGN can help to probe the relationship between very different physical components - the cool, optically thick disk and hot, optically thin corona. Here, we review the relationship between optical and X-ray variability in Seyfert galaxies, which due to observing constraints was difficult to study for many years, but was given a huge boost with the launch of the RXTE satellite in 1995. We summarise the diverse results of several monitoring campaigns, which pose a challenge for standard theories relating optical and X-ray variability, with sources showing either correlated optical and X-ray flux variations, correlated optical flux and X-ray spectral variations, or no correlation at all. We discuss possible explanations for these results, some of which may be explained using a more standard AGN picture, while others may require additional components, such as the 2-phase accretion flows suggested to explain black hole X-ray binary behaviour.