Abstract
Abstract Characteristic variability timescales in blazar γ-ray light curves can provide insights into the physical processes responsible for γ-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 light-curve simulation study, we develop a methodology to identify PSD breaks using CARMA models. Using this methodology, we study the γ-ray light curves of 13 bright blazars observed with the Fermi Large Area Telescope in the 0.1–300 GeV band over 9.5 yr. We present the blazar γ-ray PSDs, which provide evidence for low-frequency breaks on timescales ∼1 yr in four sources, and an additional high-frequency break on a timescale ∼9 days in one source.
Highlights
Blazars are a subclass of active galactic nuclei (AGNs) whose jet is oriented close to our line of sight (Antonucci 1993; Urry & Padovani 1995)
We find that the break timescales recovered from the Continuous-time autoregressive moving-average (CARMA)(1, 0) models are systematically longer than the true timescales, in the high-signal-to-noise ratio (S/N) simulations, due to an effect of binning the power spectral density (PSD)
This is observed in our simulations as well and is a consequence of the CARMA models capturing some of the white-noise behavior induced by measurement errors
Summary
Blazars are a subclass of active galactic nuclei (AGNs) whose jet is oriented close to our line of sight (Antonucci 1993; Urry & Padovani 1995). They are characterized by powerful nonthermal emission and rapid, high-amplitude variability across the electromagnetic spectrum, on timescales ranging from minutes to years. The blazar spectral energy distribution (SED) contains a low-energy component covering radio to X-ray frequencies and a high-energy component peaking in the γ-rays. Of particular interest is the γ-ray regime, where the high-energy component of the SED peaks, and which has been studied in less detail than the radio, optical, and X-ray bands. The Fermi Large Area Telescope (Fermi/LAT) blazar monitoring program (Abdo et al 2010) has provided an excellent opportunity to study the long-term γ-ray variability
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