Flux Density and VLBI Measurements of the IDV Source 0917+624

Abstract

Extragalactic compact flat spectrum radio sources are known to be highly variable and about 30% of them show intra-day variability (IDV). The quasar 0917+624 was known to show prominent IDV behaviour from the time it was first studied as a short-time variable source. Meanwhile, however, its variability ceased and yet the reason for that is not clear. The working hypothesis for the observations, on which the main part of this thesis is based, was that structural changes of the variable part of the source have caused the variability decline. These changes could be revealed using high resolution observing techniques, namely VLBI.<br /> Several epochs of single-dish flux density measurements performed with the Effelsberg 100m radio telescope between 2001 and 2004 as well as several multi-frequency epochs of VLBI observations of 0917+624 over a period of eight years (1999 to 2007) have been analysed concerning particularly kinematic and polarimetric properties and the results are interpreted in terms of Intraday Variability.