JETS in Active Galactic Nuclei

Abstract

Radio jets are a common feature of radio-loud AGN, and provide a means for powering the luminous giant radio lobes which first marked the extreme activity in AGN. Some jets have complicated, filamentary structures, and many show evidence of bulk relativistic motion on small (pc) and possibly large (kpc) scales. A general picture has emerged in which all radio-loud AGN have relativistic jets, which are, or can appear to be, different for the various classes of AGN. Recent observations at wavelengths shorter than the radio, principally with space observatories like HST, IUE, GRO and Rosat, have provided a wealth of new information about the origin and structure of jets. High-resolution HST images of resolved jets like M87 indicate the likely importance of shocks that can accelerate radiating particles to very high energies. Detailed comparison of UV images with radio maps of comparable resolution reveals many similarities and some important differences in morphology. For the larger number of jets too small to be imaged from Earth, variability studies, with IUE and Rosat in particular, and the very high energy gamma-ray emission detected with GRO, have given new insight into the formation and internal energetics of jets. The recent multiwavelength monitoring campaign on the BL Lac object PKS 2155-304 and ongoing multiwavelength monitoring of other blazars offer the best hope of understanding the jets, and ultimately the central power source, in AGN.