Although the emphasis of this thesis was on the ``Whole-Sky'' sample, two related investigations included in this thesis have produced significant results. The first of these was the comparison of the VLBI properties of the EGRET-identified radio sources with the VLBI properties of similar radio sources not identified by EGRET. This work was prompted by the identification of PKS 0521-365 by EGRET. The properties which were compared were the apparent speeds in VLBI jets, the radio core brightness temperatures and pc-scale to kpc-scale jet misalignment angles. These properties are indicators of relativistic beaming which might be used to determine the differences or similarities in the beaming properties between the populations of gamma-ray loud and quiet radio sources. Relativistic beaming lies at the heart of many models for AGN gamma-ray emission.
The comparison in chapter 4 finds no significant evidence to support a difference in the beaming properties based on apparent jet speeds or misalignment angles. Some evidence exists suggesting that EGRET-identified radio sources have higher radio core brightness temperatures than similar radio sources not identified by EGRET. The comparison was based on new observations and observations from the literature.
A strong conclusion of the work was that a very wide variety of properties are associated with gamma-ray radio sources, and that a one-to-one relationship between beamed radio emission and beamed gamma-ray emission is not tenable.
The second additional investigation was the study of GRO J1655-40 with the SHEVE array. GRO J1655-40 was discovered as a new, bright X-ray source with BATSE on 1994 July 27. The SHEVE array was used to image the compact radio source which subsequently appeared.
The SHEVE observations revealed a jet-like structure which expanded at the rate of 65 mas/day, causing difficulties in the data reduction which were overcome by reducing the size of the imagable data sets. The high angular rate was confirmed. With distance measurements the angular motion corresponded to an apparent speed of expansion of between 1.1 and 1.9 times the speed of light. GRO J1655-40 was the second Galactic superluminal source to be discovered after GRS 1915+105. Taking the geometry of the GRO J1655-40 jet into account, the intrinsic speed was shown to be at least mildly relativistic.
The combination of multi frequency observations with the SHEVE and other VLBI observations reveal a strong empirical link between the accretion of material onto a compact mass and the production of relativistic jets.