Statistics of intraday variability in extragalactic radio sources

Abstract

Intraday variations with amplitudes ranging up to ∼ 25% have been found in several compact extragalactic radio sources. Here the results of a search for such variations in two complete samples of flat-spectrum sources are presented. Low-level fluctuations are found in virtually all sources that have a compact VLBI structure ; this result is compatible with the expectation that the influence of refractive interstellar scintillation should be detectable on the 1-2% level