Characteristic Variability Timescales in the Gamma-ray Power Spectra of Blazars

TL;DR

This paper develops a methodology using CARMA models to identify characteristic variability timescales in blazar gamma-ray light curves, revealing significant PSD breaks on year-long and day-long timescales in several sources.

Contribution

It introduces a new approach to detect PSD breaks in blazar gamma-ray data using CARMA models, applied to Fermi-LAT observations.

Findings

Detection of ~1 year PSD breaks in four blazars

Identification of a ~9 day PSD break in one blazar

Methodology improves understanding of blazar variability mechanisms

Abstract

Characteristic variability timescales in blazar gamma-ray light curves can provide insight into the physical processes responsible for the gamma-ray variability. The power spectral density (PSD) is capable of revealing such timescales, which may appear as breaks or periodicities. Continuous-time autoregressive moving-average (CARMA) models can be used to accurately estimate a light curve's PSD. Through a lightcurve simulation study, we develop a methodology to identify PSD breaks using CARMA models. Using this methodology, we study the gamma-ray light curves of 13 bright blazars observed with the Fermi Large Area Telescope in the 0.1-300 GeV band over 9.5 years. We present the blazar gamma-ray PSDs, which provide evidence for low-frequency breaks on timescales ~1 year in four sources, and an additional high-frequency break on a timescale ~9 days in one source.