A multiwavelength study of blazars

Blazars are generally defined as the subset of quasars exhibiting collimated, relativistic jets pointing very close to our line of sight and emitting a significant fraction of their detected luminosity in Gamma-rays. In this thesis, I develop a new technique for identifying blazar counterparts for Gamma-ray sources detected by the Energetic Gamma-Ray Experiment Telescope (EGRET) compiled in the Third EGRET Catalog (3EG) based on their radio/X-ray properties. Using recent VLA radio data, I apply this selection criteria to ∼75% of the sky. In this region I increase the fraction of EGRET sources with identified counterparts significantly, from ∼40% to ∼70%. Additionally, I show that blazar counterparts for EGRET detections can be selected with a high degree of confidence down to radio fluxes an order of magnitude less than previously believed. My optical spectroscopic follow-up at McDonald Observatory provides new classification and redshifts for ∼three dozen EGRET counterparts.; In preparation for the next generation Gamma-ray satellite, the Gamma-ray Large Area Space Telescope (GLAST), I extend this technique beyond the 3EG catalog. In particular, I have created a survey of blazar candidates selected to have radio/X-ray properties similar to those of the 3EG blazar counterparts. I show that these blazar candidates show a significant positional correlation with excesses in the residual EGRET photon counts map when the 3EG sources are subtracted. In the course of the survey the highest redshift blazar to date was discovered. Finally, based on these new EGRET identifications, I extrapolate the distribution of this blazar population to the GLAST 1-year survey flux threshold, providing an updated estimate of source counts.