High Energy Emission from Blazars

Abstract

Blazars, a subclass of AGN, include BL Lac objects and OVV quasars. These objects axe characterized by non-thermal continuum spectra and strong time variability, with pronounced occasional flaring in most observable wavelengths. One of their defining characteristics is high polarization in the radio and optical spectral regimes (cf. Angel & Stockman 1980). In the radio band, VLBI studies of these objects show compact radio structures on milli-arcsecond angular scale. These jet-like structures often show superluminal motion, where individual components are observed to move away from the radio cores with the apparent speed v/c of a few (see, e.g., Vermeiden & Cohen 1994).