Fourier Analysis of Blazar Variability

TL;DR

This paper introduces a new theoretical model based on electron transport equations in the Fourier domain to explain blazar variability, successfully reproducing observed PSDs and predicting specific behaviors across different emission components.

Contribution

The paper develops a novel Fourier domain model incorporating electron cooling and escape, providing new insights into blazar variability and emission properties.

Findings

Model reproduces observed PSD shapes across multiple bands.

Predicts PSD and time lag behaviors for different emission components.

FSRQs have steeper PSD indices than BL Lacs at low frequencies.

Abstract

Blazars display strong variability on multiple timescales and in multiple radiation bands. Their variability is often characterized by power spectral densities (PSDs) and time lags plotted as functions of the Fourier frequency. We develop a new theoretical model based on the analysis of the electron transport (continuity) equation, carried out in the Fourier domain. The continuity equation includes electron cooling and escape, and a derivation of the emission properties includes light travel time effects associated with a radiating blob in a relativistic jet. The model successfully reproduces the general shapes of the observed PSDs and predicts specific PSD and time lag behaviors associated with variability in the synchrotron, synchrotron self-Compton (SSC), and external Compton (EC) emission components, from sub-mm to gamma-rays. We discuss applications to BL Lacertae objects and to flat-spectrum radio quasars (FSRQs), where there are hints that some of the predicted features have already been observed. We also find that FSRQs should have steeper PSD power-law indices than BL Lac objects at Fourier frequencies < 10^{-4} Hz, in qualitative agreement with previously reported observations by the Fermi Large Area Telescope.