Abstract: The class of active galactic nuclei termed 'blazars' displays dynamic plasma jets aligned close to the line of sight of the observer. The launching, collimation, acceleration to relativistic flow speeds, and sustainment of these powerful jets is a primary current question in astrophysics. Multiwavelength observations, which probe within a few parsecs of the supermassive black hole, can reveal the mechanisms behind this emission. Blazar jets are well-observed at radio wavelengths; the angular resolution at 43 GHz with the Very Long Baseline Array corresponds to less than a parsec for many objects. We can examine flux density and polarization data to gain insight into the magnetic field alignment, jet shape, knot speeds, and other physical properties. However, at optical wavelengths, blazars are only resolved on a length scale of kiloparsecs. Thus, the location of higher-frequency emission on parsec scales needs to be inferred rather than directly observed. A new technique allows a connection to be made between high-frequency emission and the parsec-scale jet by comparison of polarization characteristics. If the optical electric vector position angle (EVPA) value is close to that of a feature in the radio jet, we can conclude that the emission at both wavelengths is produced by the same mechanism in the same general location. Our work expands this technique by using measurements of time variability during two intensive 10-day multiwavelength campaigns. The study of this data set determines the correlation in variability between the optical EVPA and that at 43 GHz in the parsec-scale jet. This dissertation establishes cospatiality of optical emission with the stationary core seen in 43 GHz images for the majority of our sample of 20 blazars by finding that the EVPAs of the two wavebands agree in value as well as in the timing and manner of their variation. The work then focuses on the magnetic field structure in and around the blazar core. A model is constructed for the production of polarization in each object, and these models are compared to determine the physical nature and structure of the core for blazars as a whole.

The existence of jets emanating from the central sources of radio galaxies and quasars was perhaps the most important discovery for our understanding of the nature of active galactic nuclei. These proceedings present reviews and research papers on extragalactic radio sources. The book begins witha discussion of the phenomenology and models of radio sources. The main partis devoted to detailed studies of jets by VLBI, to the information obtained about the structure of the central source as deduced from variability studies, to production, confinement and velocity of jets as well as to numerical simulations of the jet phenomenon. Reviews of the two best studied jets - those in the radio galaxy M87 and the quasar 3C273 - illustrate our current observational picture of extragalactic radio jets in all accessible wavelength ranges. A section on the influence of the environment on radio galaxies concludes the book. This topical volume addresses researchers and graduate students in astrophysics.

Blazars (also known as BL Lac objects), first discovered in 1978, are unusually energetic objects in the extragalactic universe. About 200 are known or suspected. They are radio sources with highly variable optical and radio emission, as well as high polarisation, and their optical spectra normally have no distinguishable features. It is generally accepted that they belong to that class of galaxies with active galactic nuclei, which are presumed to be driven by infall of matter to a supermassive black hole. In this book researchers give a complete summary of the observations of blazars and the theoretical interpretation. A comprehensive listing of confirmed and candidate objects is included. Mechanisms in which the variability can arise from shocks and relativistic jets are discussed. There are at least four different answers given to the question: what is a blazar? This book is a complete overview of the violent activity observed in these extreme active galactic nuclei.

Quasars and active galaxies are the most powerful emitters of radiation in the universe. Modern radio telescope arrays have shown that the ultimate energy source resides in the central few parsecs of the galactic nucleus, and powers the emitting regions by way of two oppositely-directed relativistic jets of energy. This volume presents the latest observations and theories of these remarkable objects. Topics discussed include superluminal motions, the physics of jets and shock fronts in jets, related optical observations, and cosmic evolution. Particular attention is given to the "unified theories," which attempt to show that many of the phenomena in powerful extragalactic objects are different aspects of a single, basic mechanism; the main difference in their appearance is a result of their different orientation with respect to the observer.

Written by a carefully selected consortium of researchers working in the field, this book fills the gap for an up-to-date summary of the observational and theoretical status. As such, this monograph includes all used wavelengths, from radio to gamma, the FERMI telescope, a history and theory refresher, and jets from gamma ray bursts. For astronomers, nuclear physicists, and plasmaphysicists.

An up-to-date study of astrophysical jets that will appeal to students and researchers in all areas of astrophysics.