The ATCA intraday variability survey of extragalactic radio sources

We present the results of an Australia Telescope Compact Array (ATCA) surve y for intraday variability (IDV) of the total and polarized flux densities of 118 compact, flat-spectrum, extragalactic radio sources from the Parkes 2.7-GHz Survey. A total of 22 total flux density IDV sources were discovere d and 15 sources were found to show IDV of their polarized flux density. We discuss the statistical properties of the IDV sources, including the distr ibution of source modulation indices, and the dependence of the variability amplitude on source spectral index and on Galactic position. We suggest in terstellar scintillation (ISS) in the Galactic interstellar medium as the m ost likely mechanism for IDV. Even so, the inferred high brightness tempera tures cannot be easily explained.