Interstellar Scintillation and Radio Intra-Day Variability

Considerable evidence has now accumulated strongly favoring interstellar scintillation as the mechanism responsible for the rapid intra-day variability seen at cm wavelengths in many flat-spectrum extragalactic radio sources. The discovery of three rapid intra-day variability sources, PKS 0405−385, PKS1267−326 and J1819+3845, has been largely responsible for this new paradigm. We present here recent results for the two southern sources PKS0405−385 and PKS1257−326, together with observations and first results from the MASIV (Micro-Arcsecond Scintillation-Induced Variability) survey that we are undertaking at 5GHz with the VLA.