The characteristics of variability of AGNs based on the structure function

TL;DR

This study uses the structure function to analyze AGN variability across radio, optical, and gamma-ray bands, revealing different physical mechanisms and distinguishing between AGN types and Fermi classifications.

Contribution

It introduces an improved structure function method with integrated parameters to effectively differentiate AGN variability across multiple bands and classify AGN types.

Findings

Structure function effectively distinguishes variability in radio, optical, and gamma-ray bands.

BL Lacs and FSRQs can be distinguished using the structure function parameters.

Differences between Fermi and non-Fermi FSRQs are significant, but not between Fermi and non-Fermi BL Lacs.

Abstract

Variability is one of the classic features of active galactic nuclei (AGNs). The normalized structure function was applied to distinguish variability samples from OVRO, ASAS-SN and Fermi. A power-law function model was selected to fit the structure functions of samples of three bands. We present the available samples of three bands, and by integrating two parameters, we obtain ideal discrimination results for three bands. Meanwhile, the differences between BL Lacs and FSRQs of Fermi and non-Fermi samples are well verified. The results show that the improved structure function can effectively distinguish samples of radio, optical, and gamma-ray. Additionally, BL Lacs and FSRQs in both Fermi and non-Fermi samples can be distinguished. The conclusion obtained through the distinction of structural functions in different bands supports that the variability in the three bands are caused by different physical mechanisms respectively: the samples in the optical band are radio quiet AGNs, and their variability is mainly caused by the fluctuations of the accretion disk, and the samples of radio band and gamma-ray band are radio loud AGNs whose variability is mainly caused by relativistic jet radiation. This conclusion conforms to the unified standard interpretation of variability about AGNs. Using these two parameters, we verify that there is no fundamental difference between Fermi and non-Fermi BL Lacs, while significant differences exist between FSRQs. However, the power exponent of the two can well distinguish BL Lacs.