Gamma-ray Flux Distribution and Non-linear behavior of Four LAT Bright AGNs

TL;DR

This study statistically characterizes gamma-ray emission from four bright AGNs, revealing non-linear variability patterns and suggesting a multiplicative process, with implications for jet physics and central engine connections.

Contribution

It provides the first detailed statistical analysis of gamma-ray flux distributions and variability in four bright AGNs, highlighting non-linear behavior and potential physical models.

Findings

Blazars' flux distributions are consistent with a lognormal, indicating non-linear variability.

Flux-rms relation is linear for three blazars, supporting multiplicative variability.

Power spectra suggest scale-free shot noise with possible break points.

Abstract

We present a statistical characterization of the $\gamma$-ray emission from the four \emph{Fermi}-LAT sources: FR I radio galaxy NGC 1275, BL Lac Mrk 421, FSRQs B2 1520+31 and PKS 1510-089 detected almost continuously over a time integration of 3-days between August 2008 - October 2015. The observed flux variation is large, spanning $\gtrsim 2$ orders of magnitude between the extremes except for Mrk~421. We compute the flux distributions and compare with Gaussian and lognormal ones. We find that the 3 blazars have distribution consistent with a lognormal, suggesting that the variability is of a non-linear, multiplicative nature. This is further supported by the computation of the flux-rms relation, which is observed to be linear for the 3 blazars. However, for NGC 1275, the distribution does not seem to be represented either by a lognormal or a Gaussian, while its flux-rms relation is still found to be linear. We also compute the power spectra, which suggest the presence of a break, but are consistent with typical scale-free power-law shot noise. The results are broadly consistent with the statistical properties of the magnetic reconnection powered minijets-in-a-jet model. We discuss other possible scenarios and implications of these observations on jet processes and connections with the central engine.