Radio-emitting Plasma Research Articles

Semidynamical models of radio jets - Relativistic beaming and source counts

VLBI observations of compact radio sources exhibit core-jet structure and apparent superluminal expansion. Both features can be produced by a relativistic jet of radio-emitting plasma beamed toward the observer. This model implies that there should be several fainter unbeamed sources for every beamed source. Partial luminosity functions (the probability distribution functions for the observed flux from a source at a given distance viewed from different directions) are calculated for different relativistic jet models. Kinematical models that approximate relativistic shock fronts are emphasized. These differ from the kinematically simpler models which are usually invoked, in that the velocity of the emitting fluid, which is responsible for the Doppler boosting, is distinct from the velocity of the pattern, which is responsible for the superluminal motion. Numerical calculations of the emission from semidynamical shock models demonstrate that a wide range of partial luminosity functions can be produced. It is concluded that source counts cannot be used as precise probes of relativistic beaming and are of limited use in testing the beaming hypothesis. 27 references.

Peculiar radio structure in the quasar 3C380

The majority of powerful extragalactic radio sources have steep radio spectra and angular sizes >5 arc s. Their basically symmetrical double structures can be explained by means of two, originally antiparallel, beams which emanate from a massive object or central engine (CE) and transport energy to the ‘outer lobes’ some 105–106 pc away1. Around one-third of sources, however, are more compact. The flat-spectrum compact sources may be part of the same parent population as the steep-spectrum extended sources but observed end-on rather than broadside-on2,3. As yet, however, we have little understanding of the steep-spectrum compact sources (SSCSs) which have recently been shown to comprise ∼30% of all steep-spectrum objects4,5. We now present radio maps which hint at an explanation for the small size of at least some of these SSCSs. Our maps, of the quasar 3C380, reveal a peculiar radio structure which is difficult to interpret other than by a powerful interaction between the radio-emitting plasma and its environment. Thus, the sub-galactic (projected) dimensions of this and other SSCSs may be a result of the beams being disrupted before they have propagated beyond the parent object.