An Overview of Blazar Variability

TL;DR

This paper reviews the rapid multiwavelength variability of blazars, highlighting progress in understanding their emission mechanisms and identifying unresolved questions about seed photon origins.

Contribution

It provides an overview of recent multiwavelength monitoring campaigns and discusses the implications for blazar emission models and variability behaviors.

Findings

Multiwavelength campaigns reveal diverse blazar variability patterns.

Data suggest synchrotron and Compton processes dominate jet emission.

PKS2155-304 data challenge homogeneous source models.

Abstract

Blazars are characterized by rapid variability at virtually all wavelengths from radio through TeV gamma-rays. The challenge since their discovery has been to understand the origin of their luminous, apparently nonthermal, nuclear emission. Considerable progress has been made in recent years thanks to a handful of multiwavelength monitoring campaigns with high enough temporal sampling to resolve the most rapid variations. The best data for a few objects have shown a variety of behaviors, for the most part commensurate with synchrotron and Compton-scattered emission from a relativistic jet, though better data for more blazars are still clearly needed. In particular, the origin of the seed photons that are upscattered to gamma-ray energies remains unclear. The latest multiwavelength light curves for the BL Lac object PKS2155-304 appear to rule out synchrotron emission from a homogeneous source.