Exploring the Origins of Optical Variability in AGNs: Correlations with Black Hole Properties, X-ray, and Radio Emission

TL;DR

This study analyzes optical variability in AGNs over five years, examining how black hole mass, luminosity, X-ray, and radio emissions influence variability, and finds that accretion disk properties mainly drive long-term optical changes.

Contribution

It provides new insights into the dependence of AGN optical variability on black hole and accretion disk parameters, with minimal influence from X-ray and radio jet activity.

Findings

Optical variability correlates positively with SMBH mass and luminosity.

No significant dependence of optical variability on X-ray properties.

Weak anti-correlation between optical variability and radio parameters.

Abstract

We study the optical variability characteristics of Active Galactic Nuclei (AGN) from the Swift Burst Alert Telescope (BAT) AGN catalogue by utilising approximately five years of optical light curves from the Zwicky Transient Facility (ZTF) survey. We investigate dependencies of the long-term optical variability amplitudes and timescales on (i) supermassive black hole (SMBH) mass, luminosity, and Eddington ratio to explore the influence of accretion disk dynamics and radiative processes; (ii) X-ray properties, such as spectral photon indices and fluxes, to study the effect of high-energy emission mechanisms; and (iii) radio characteristics, such as integrated fluxes and radio loudness, which indicate jet activity. Our findings confirm a positive correlation between the variability time scale and both the SMBH mass and luminosity, suggesting that these physical parameters significantly impact the optical variability timescale. Conversely, no significant dependence is found between optical variability and X-ray properties, indicating that high-energy processes may not substantially influence long-term optical variability. Additionally, a weak anti-correlation between optical variability and radio parameters suggests that jet activity has a negligible effect on causing long-term AGN variability. These results support the hypothesis that long-term optical variability in AGN is primarily governed by thermal emission from the accretion disk. Further investigations with larger samples are essential to refine these correlations and develop robust physical models integrating black hole properties, accretion disk physics, and multi-wavelength radiative transfer.