Variable Radio Sources

Abstract

Flux variations are a common feature of flat spectrum compact extra-galactic radio sources. Detailed analysis and quantitative comparisons with theoretical models (e.g. van der Laan, 1966) are difficult due to the complex characteristics of the flux variations, which generally appear to consist of different outbursts blended together in time. Nevertheless, the general consensus is that the basic process has been correctly identified and consists in an expansion of a synchrotron radiating plasma cloud of relativistic electrons and magnetic field partially opaque to its own radiation. The main differences between data and predictions of the theory are that the variations propagate too fast and with too large amplitude toward lower frequencies. This behaviour however may be indicative of continuous energy supply and consequent accelerated expansion.