This is the second in a series of papers presenting an analytical model for the evolution of FRII radio sources. In this paper we evaluate the expected radio emission from a radio source incorporating energy loss processes for the relativistic electrons. By combining these results with our earlier dynamical model we calculate evolutionary tracks through the Power-Linear size diagram. These tracks are in good agreement with the observed distribution of sources in this diagram. The effects of different forms for the evolution of the magnetic field in the cocoon, the redshift of the source, the environment of the source and the defining parameters of the jet are investigated. The evolutionary tracks are found to be insensitive to the assumed form of the magnetic field evolution. Some evidence against protons as a major constituent of the jet material is also found.

Winged, or X‐shaped, radio sources form a small class of morphologically peculiar extragalactic sources. We present multifrequency radio observations of two such sources. We derive maximum ages since any re‐injection of fresh particles of 34 and 17 Myr for the wings of 3C 223.1 and 3C 403 respectively, based on the lack of synchrotron and inverse Compton losses. On morphological grounds we favour an explanation in terms of a fast realignment of the jet axis which occurred within a few Myr. There is no evidence for merger activity, and the host galaxies are found to reside in no more than poor cluster environments. A number of puzzling questions remain about those sources: in particular, although the black hole could realign on sufficiently short time‐scales, the origin of the realignment is unknown.

We report on the discovery of a source that exhibits over 300% amplitude changes in radio flux density on the period of hours. This source, J1819+3845, is the most extremely variable extragalactic source known in the radio sky. We believe these properties are due to interstellar scintillation and show that the source must emit at least 55% of its flux density within a radius of fewer than 16 µas at 5 GHz. The apparent brightness temperature is greater than 5x1012 K, and the source may be explained by a relativistically moving source with a Doppler factor of approximately 15. The scattering occurs predominantly in material only a few tens of parsecs from the Earth, which explains its unusually rapid variability. If the source PKS 0405-385 is similarly affected by local scattering material, Doppler factors of approximately 1000 are not required to explain this source. The discovery of a second source whose properties are well modeled by interstellar scintillation strengthens the argument for this as the cause for much of the variation seen in intraday variables.

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Abstract. We present two years of monitoring observations of the extremely variable quasar J1819+3845. We observe large yearly changes in the timescale of the variations (from ∼1 hour to ∼10 hours at 5 GHz). This annual effect can only be explained if the variations are caused by a propagation effect, and thus affected by the Earth's relative speed through the projected intensity pattern. To account for this effect, the scattering plasma must have a transverse velocity with respect to the local standard of rest. The velocity calculated from these observations is in good agreement with that obtained from a two telescope delay experiment (Dennett- . We also show that either the source itself is elongated, or that the scattering plasma is anisotropic, with an axial ratio of >6:1. As the source is extended on scales relevant to the scattering phenomenon, it seems plausible that the anisotropy is due to the source itself, but this remains to be investigated. From the scintillation characteristics we find that the scattering material is a very strong, thin scatterer within ∼ten parsecs. We determine a source size at 5 GHz of 100 to 900 microarcsecs, and associated brightness temperatures of 10 10 to 10 12 K.