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

Abstract

Characteristic variability timescales in blazar γ-ray light curves can provide insight into the physical processes responsible for the γ-ray variability. The power spectral density (PSD) is capable of revealing such timescales, which may appear as breaks or periodicities. Continuous-time autoregressive movingaverage (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 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 years. We present the blazar γ-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.

A comprehensive power spectral density analysis of astronomical time series I: the Fermi-LAT gamma-ray light curves of selected blazars

“…We employ BIC, and choose the simplest model (i.e., with lowest p) within the band ∆ i < 2 as the best fit. Our results, summarized in Table 7, are generally in agreement with Ryan et al (2019). In the case of 7 d binning of PKS 2155−304, when restricted only to CARMA(p, p − 1), we also obtain p = 2 as the best, and p = 1 as the simplest model within ∆ i < 10.…”

“…It is worth mentioning that the index does not depend on the redshift or blazar classification. Recently, Ryan et al (2019) analyzed long-term (9.5 years) daily-and weekly-binned Fermi -LAT LCs (taken from the Fermi Science Support Center 1 ) of 13 blazars previously studied by Sobolewska et al (2014). The LCs were analyzed with the continuous-time autoregressive moving average (CARMA) model (Kelly et al 2014), indicating that the OU processes, i.e.…”

A Decade of Multiwavelength Observations of the TeV Blazar 1ES 1215+303: Extreme Shift of the Synchrotron Peak Frequency and Long-term Optical–Gamma-Ray Flux Increase

“…The SuF curve drops to zero at indices of 0.3 and 0.9. This suggests that the PSD distribution is relatively flat compared to the typical values between one and two found in AGNs (e.g., Uttley et al 2002;Sobolewska et al 2014;Ryan et al 2019).…”

AGN variability in the age of VRO

“…In addition, radio variability can also be intrinsic, and if so comes from the inner core of the AGN [15]. The variability from higher frequency light can occur on timescales between minutes and years [16][17][18], while lower frequency light tends to occur on the scales of months to years [19]. At the higher end of the variability timescale are changing-look AGN, whose intensity can fluctuate over time periods of decades [20][21][22].…”