EGRET (GeV) Blazars

The EGRET instrument on the Compton Gamma Ray Observatory (1991-2000) has positively detected high energy γ-ray emission from more than 67 active galaxies of the blazar class. The majority of the EGRET blazars are flat-spectrum radio quasars, which are characterized by inferred isotropic luminosities often as high as 3×10⁴⁹ ergs s^-1. The remainder are BL Lac objects, some of which have been detected at TeV energies (>250 GeV) by ground-based atmospheric Cherenkov telescopes. One of the remarkable characteristics observed in blazars is that the γ-ray luminosity often dominates the bolometric power in these sources. The detection of blazars by EGRET has undoubtedly been one of the highlights of the mission, and has forever impacted our understanding of the emission mechanisms in these objects. In this article, we summarize the properties of EGRET blazars, and review the constraints that the EGRET observations place on the various models of γ-ray production in these sources. .