Donskykh G. The structure of the temporal changes in fluxes of extragalactic radio sources and their connection with the data of VLBI observations.

This dissertation presents a study of the radio flux density variations in active galactic nuclei. The monitoring data at 14.5, 8 and 4.8 GHz obtained with the 26-m radio telescope over a 40-year period were provided by The University of Michigan Radio Astronomy Observatory (UMRAO). The study focuses on the investigation of radio galaxies 3С120 and 3С273, quasars 3С345, 3С454.3, DA55 and CTA102, as well as blazars 3С446, BL Lac and OJ287. The study was performed using the Singular Spectrum Analysis technique which enabled to detect the periodicity of the investigated time series with high accuracy. The study resulted in the periods of the flux density variability in the time intervals from 1.3 to 10.5 years for the radio galaxy 3C120; 2.3 to 8.6 years for the radio galaxy 3C273; 2.8 to 16.4 years for the quasar 3C345; 1.9 to 10.3 years for the blazar 3C446; 1.7 to 6.6 years for the quasar 3C454.3; 1.8 to 8.2 years for the blazar BL Lac; 1.1 to 1.6 years for the blazar OJ287; 1.1 to 3.9 years for the quasar CTA102, and 0.5 to 2.3 years for the quasar DA55. The VLBI images obtained from the MOJAVE program have been examined during the research. Based on the performed analysis of quasi-periodic flux variations, the combination of periods at 14.5 GHz which resulted in different phases of activity, as well as the associated radio image of the source, was successfully determined. The dissertation also considers the study of changes in the positions of some jet components relative to the VLBI-core of the investigated objects. The jet components of the sources 3С120, 3С446, 3С454.3, BL Lac, OJ287, CTA102 and DA55 exhibit complex trajectories of the changes in their positions which may be indicative of the reverse shock-wave passage. The positions of the jet components of the radio galaxy 3C273 and quasar 3C345 change predominantly in the near-radial direction.