Fourier Analysis of Blazar Variability: Klein-Nishina Effects and the Jet Scattering Environment

Abstract

The strong variability of blazars can be characterized by power spectral densities (PSDs) and Fourier frequency-dependent time lags. In previous work, we created a new theoretical formalism for describing the PSDs and time lags produced via a combination of stochastic particle injection and emission via the synchrotron, synchrotron self-Compton, and external Compton (EC) processes. This formalism used the Thomson cross section and simple $\delta$-function approximations to model the synchrotron and Compton emissivities. Here we expand upon this work, using the full Compton cross section and detailed and accurate emissivities. Our results indicate good agreement between the PSDs computed using the $\delta$-function approximations and those computed using the accurate expressions, provided the observed photons are produced primarily by electrons with energies exceeding the lower limit of the injected particle population. Breaks are found in the PSDs at frequencies corresponding to the cooling timescales of the electrons primarily responsible for the observed emission, and the associated time lags are related to the difference in electron cooling timescales between the two energy channels, as expected. If the electron cooling timescales can be determined from the observed time lags and/or the observed EC PSDs, then one could in principle use the method developed here to determine the energy of the external seed photon source for EC, which is an important unsolved problem in blazar physics.

10 pages, 5 figures. Accepted by ApJ

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• The Great Markarian 421 Flare of February 2010: Multiwavelength variability and correlation studies
• Time-Dependent Electron Acceleration in Blazar Transients: X-Ray Time Lags and Spectral Formation
• Particle diffusion and localized acceleration in inhomogeneous AGN jets - Part II: stochastic variation
• Blazar variability power spectra from radio up to TeV photon energies: Mrk 421 and PKS 2155-304
• The long-term centimeter variability of active galactic nuclei: A new relation between variability timescale and accretion rate
• Electron Acceleration In Blazars: Application to the 3C 279 Flare on 2013 December 20
• Simulations of Stochastic Long-Term Variability in Leptonic Models for External-Compton and Synchrotron Self-Compton Dominated Blazars
• Optical variability modeling of newly identified blazar candidates behind Magellanic Clouds
• Searching for signatures of chaos in gamma-ray light curves of selected Fermi-LAT blazars
• Progress in Multiwavelength and Multi-Messenger Observations of Blazars and Theoretical Challenges
• X-ray Fourier lag-frequency spectra modulated by stochastic turbulent acceleration in the jets of high-frequency-peaked BL Lac
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