The Physics of Blazar Jets

Abstract

Abstract Because blazars are characterized by beamed emission from relativistic jets aligned with our line of sight, they are ideal sources for studying jet physics. Over the past few years, multiwavelength monitoring of dozens of blazars with the Fermi gamma-ray telescope and optical-infrared telescopes has revealed a close correlation between the synchrotron and high-energy components of blazar spectral energy distributions. This strongly supports a model for the emission mechanism in which gamma-rays are produced when synchrotron-emitting electrons Compton up-scatter ambient synchrotron or thermal photons. Flat-spectrum radio quasars also have a blue, less variable component that is likely to be thermal emission from a slowly varying accretion disk, while BL Lacs have only weak or radiatively inefficient disks. The temporal symmetry of gamma-ray and optical-infrared flares implies that the variability time scales are dominated by light crossing times or the passage of a disturbance through the emission region rather than by the acceleration or energy-loss timescales of the radiating electrons. This new understanding of jet physics for a sizeable blazar sample allows us to refine estimates of jet power, which is important for understanding jet formation and for feedback onto galaxies and the intergalactic medium.