Characterizing the origins of gamma-ray variability of the jetted active galactic nuclei observed with the Fermi-LAT

TL;DR

This study analyzes gamma-ray variability in jetted AGNs using Fermi-LAT data, revealing variability timescales, emission region locations, and correlations with jet and accretion properties.

Contribution

It provides new insights into the origins and characteristics of gamma-ray variability in jetted AGNs, including emission region localization and variability correlations.

Findings

Mean variability damping timescale ~100 days.

FSRQs show greater variability than BL Lacs.

Gamma-ray emission region likely beyond the BLR, near the dusty torus.

Abstract

We conducted an analysis of gamma-ray variability in a large sample of jetted active galactic nuclei (AGNs) by utilizing archival Fermi-LAT light curves and applying damped random walk modeling to obtain variability amplitude. Our primary findings are summarized as follows: (1) The mean variability damping timescales of our sources are approximately 100 days. This damping timescale may imply that the diffusive shock acceleration plays an important role in the variability of gamma-ray emission. (2) Flat-spectrum radio quasars (FSRQs) demonstrate greater variability amplitude compared to BL Lacertae objects (BL Lacs). (3) The ratio of the distance of the emission region from the central supermassive black hole to the dusty torus radius for our sources is $R\approx2-4.5R_{\rm DT}$. In contrast, the ratio of the distance of the emission region from the central supermassive black hole to the BLR radius for our sources is $R\approx135-295R_{\rm BLR-in}$ and $R\approx123-270R_{\rm BLR-out}$. These findings indicate that the $\gamma$-ray emission region in jetted AGNs is likely located beyond the BLR, potentially could be associated with the dusty torus. (4) A statistical correlation is observed between variability amplitude and radio luminosity, radio loudness, X-ray luminosity, X-ray loudness, gamma-ray luminosity, and gamma-ray loudness, indicating a potential relationship between gamma-ray variability and jet activity. (5) Variability amplitude also shows a statistical correlations with synchrotron peak frequency luminosity, inverse Compton peak frequency luminosity, and Compton dominance. (6) Variability amplitude also correlates with black hole mass, accretion disk luminosity, and Eddington ratio, implying that the accretion disk may also contribute to gamma-ray variability.