VLBI OBSERVATIONS OF GAMMA-RAY-QUIET ACTIVE GALACTIC NUCLEI - COMPARING RADIO-CORE BRIGHTNESS TEMPERATURES

We present VLBI and Australia Telescope Compact Array images and deriv e source-frame radio-core brightness temperatures for three prominent, flat-spectrum extragalactic radio sources, notable because they have not been detected as gamma-ray sources with the EGRET instrument. Radi o-core brightness temperatures are discussed as an indicator of relati vistic beaming. A comparison of source-frame radio-core brightness tem peratures for EGRET-identified and gamma-ray-quiet, radio-loud AGNs sh ows that a wide range in beaming properties is likely to exist, indepe ndent of the level of gamma-ray emission. This comparison suggests tha t, although there is a strong relationship between radio emission and gamma-ray emission in EGRET-identified AGNs, and many EGRET-identified AGNs show evidence for relativistic beaming, there is little evidence for a one-to-one correspondence between the strength of gamma-ray emi ssion and the degree of beaming of the radio emission.