Studies in Radio Source Structure: I. A Relativistically Expanding Model for Variable Quasi-Stellar Radio Sources

Abstract

The rapid variations in the flux from some quasars at centimetre wavelengths are known to be incompatible with most models of these objects which assume that they emit synchrotron radiation and are at cosmological distances. We show that this difficulty can be resolved if the sources expand relativistically. The flux variations from a source of synchrotron radiation expanding with a velocity ∼ c can, in principle, be arbitrarily rapid. It is argued that relativistic explosive velocities could in fact arise in compact radio sources, and that models of this kind, with reasonable parameters, could account for the observed radio fluctuations of quasars.