Sergeev S. Emission line – continuum correlations in active galactic nuclei.

The thesis is devoted to the analysis of the observational relationships between broad line and continuum emission in active galactic nuclei (AGN). The results of the thesis is based on the analysis of the observational data obtained by author and by his colleagues at the CrAO in 1992–2007 together with other data sources. There are long-term changes in the relationship between line and continuum fluxes. It is confirmed that different lines respond differently to the continuum flux changes. The line responses depend on the line-of-sight velocity and on the duration of the continuum events. It is confirmed that profile variations are independent of the continuum variations. The Baldwin effect in the H-beta line is discovered and the strength of this effect is measured. The estimates of the broad-line region sizes and the central black hole masses are first obtained (or improved) for 13 AGNs by the reverberation mapping method and in terms of both the CrAO and international efforts. This facilitate to improve the “mass– luminosity” and “radius– luminosity” relationships and the position of individual types of AGNs on these diagrams. It is shown that the observed flux variability in AGNs evidences in favor of a model in which the optical and ultraviolet emission has a thermal origin, and the heating of the disk is mainly due to X-ray emission from the vicinity of the black hole. In particular, it is first found a lag between flux variations in the B, V , R, and I bands from a sample of 14 AGNs.