Exploring the variability properties of gamma-ray emission from blazars

TL;DR

This study analyzes decade-long gamma-ray observations of 20 blazars, revealing log-normal flux distributions, flicker noise variability, and quasi-periodic oscillations, providing insights into emission regions and underlying processes.

Contribution

It is the first comprehensive variability analysis of blazars combining multiple methods to identify statistical properties, quasi-periodic oscillations, and deterministic components in gamma-ray emission.

Findings

Gamma-ray flux distribution is log-normal.

Variability follows flicker noise, indicating long-memory processes.

Detected year-scale quasi-periodic oscillations in several sources.

Abstract

We present results of variability study of a sample of 20 powerful blazars using Fermi/LAT (0.1--300 GeV) observations. We studied decade-long observations applying various analysis tools such as flux distribution, symmetry analysis, and RMS-flux relation. It was found that the $\gamma$-ray flux distribution closely resembles a log-normal probability distribution function and can be characterized by linear RMS-flux relation. The power spectral density analysis shows the statistical variability properties of the sources as studied are consistent with flicker noise, an indication of long-memory processes at work. Statistical analysis of the distribution of flux rise and decay rates in the light curves of the sources, aimed at distinguishing between particle acceleration and energy-dissipation timescales, counter-intuitively suggests that both kinds of rates follow a similar distribution and the derived mean variability timescales are on the order of a few weeks. The corresponding emission region size is used to constrain the location of $\gamma$-ray production sites in the sources to be a few parsecs. Additionally, using Lomb-Scargle periodogram and weighted wavelet z-transform methods and extensive Monte Carlo simulations, we detected year-timescale quasi-periodic oscillations in the sources S5 0716+714, Mrk 421, ON +325, PKS 1424-418, and PKS 2155-304. We also performed recurrence quantification analysis of the sources and directly measure the deterministic quantities, which suggest that the dynamical processes in blazars could be a combination of deterministic and stochastic processes, while some of the source light curves revealed significant deterministic content.