High-Resolution Study of Selected Intraday Variable Sources

Abstract

Radio waves are affected by the ionized interstellar medium through which they pass. Wide ranges of scattering effects can occur and influence the observed characteristics of compact radio objects. Distinguishing between scattering-induced and source-intrinsic phenomena is very important both in studying the interstellar matter of the Milky Way and in investigating the physical properties of the background source itself. <br /> 20-25% of flat spectrum extragalactic radio sources exhibit Intraday Variability, which is thought to be at least partly due to interstellar scintillations. This phenomenon is still not understood completely. Can propagation effect alone account for all of the observed variability characteristics? How important is the contribution from the intrinsic structure of the source? What is the mixing ratio between extrinsic and intrinsic effects? In what extent are the radio observations of Active Galactic Nuclei influenced by the interstellar matter of the Milky Way?<br /> In this thesis, these questions are investigated through different observational approaches: IDV observations of selected samples of flat spectrum radio sources are presented. The dependence of variability characteristics on the galactic latitude is discussed.<br /> The interplay between extrinsic and source intrinsic effects is studied in detail for a specially selected scatter broadened quasar using single dish and interferometric measurements.<br /> Investigating the milliarcsecond to sub-milliarcsecond structure of an IDV source at the highest angular resolution in closely-spaced epochs in time can reveal the possible changes in the source structure on IDV time-scales. Space-VLBI data of total and polarized intensity of an IDV blazar are analyzed and discussed.