Multi-frequency analysis of intraday variable radio sources

Abstract

Active Galactic Nuclei (AGN) are known to show significant flux density variability across the whole electromagnetic spectrum on a wide range of time scales, from years to less than one day. In the radio regime, variability on intra-day time scales (IDV) was discovered in the mid-eighties. Due to small source sizes, either refractive interstellar scintillation (RISS) or source-intrinsic effects or a mixture of both are possible causes for IDV.<br /> Combining new observations with the 15-years IDV monitoring at the 100-m Ef-felsberg radio telescope, we performed a statistical analysis of the phenomenon. Furthermore, we tested various high frequency approaches to search for rapid variability of flat-spectrum radio sources in total intensity and polarization in the millimeter and sub-millimeter regimes. Finally, we discussed the overall interpretation of the results and some implications concerning the physics of compact structures and the characteristics of the interstellar medium.