Published in "Astrophysical Jets", eds. D. Burgarella, M. Livio and C. P. O'Dea, 1993

Abstract. Parsec-scale radio jets in radio-loud AGN connect the central region with the more extended jet and lobes. The sizescales of these compact jets are sufficiently small that the brightness, spectrum, polarization, and structure are observed to vary in most sources. The morphology typically consists of a very compact "core" from which protrudes a one-sided jet defined by a series of knots of emission. While some of these knots in a few sources are stationary, most are found to move outward along the jet at apparently superluminal speeds. The radio core is probably much larger than the region where the jet originates (the "base" of the jet). There is most likely an "inner jet" that extends from the base to the radio core yet is too small and opaque to be detected in VLBI images. Multifrequency monitoring observations from radio to -ray frequencies provide the best opportunity to explore the nature of this inner jet.

Table of Contents

INTRODUCTION

VLBI OBSERVATIONS OF COMPACT JETS

VARIABILITY OF THE FLUX DENSITY AND POLARIZATION OF EXTRAGALACTIC SOURCES

THE RELATIVISTIC JET MODEL

THE INNER JET

CONCLUSIONS

REFERENCES