| The transport of angular momentum of accretion disc and the relation between the relativistic jets and accretion processes in active galactic nuclei (AGNs) are still two open problems. In this thesis, I focus on these problems and make main works as follows.A dominant factor for the angular momentum transport in the accretion disc is likely the turbulent motions. The viscosity parameter α, which parame-terizes the underlying transport process, describes the efficiency of the turbulent transport. The alpha parameter also represents the scale of the largest possible turbulent cell. The a parameterization provides the basis for developing the ac-cretion disk theory and links the theory with the observations. For an optical monitoring blazar sample set whose typical minimum variability timescale is about1hour, we estimate a mean value of the viscosity parameter in their ac-cretion disk. We assume that optical variability on time-scales of hours is caused by local instabilities in the inner accretion disk. Comparing the observed vari-ability time-scales to the thermal time-scales of a-disc models, we could obtain constraints on the viscosity parameter (a) and the intrinsic Eddington ratio (Lin/LEdd=m),0.104≤α≤0.337, and0.0201≤Lin/LEdd≤0.1646. It can be noted that the range of a values obtained by us lies in the range predicted by current numerical simulations of MHD turbulent discs and some theoretical expected (0.1-0.3). Moreover we can find our results are consistent with obser-vational evidence0.1≤α≤0.4. On the other hand, it is much tighter, which could eliminate some models or confirm some models. This very narrow range seems to suggest that all these blazars which are observed by us are in a single "state". Hence we obtained a new evidence of the unification of flat-spectrum radio quasars (FSRQs) and BL Lac objects into a single blazar population.Blazars are a brightest and most variable subclass of AGNs. the radiation of blazars mainly come from the jet. On the other hand, the broad line region is ionized by the ionizing radiation coming from central accretion disk. An effective approach to study the link between these two phenomena is to explore the relationship between line-emission and jet kinetic power at different scales. Using a large sample consisting of70blazars with information on their K-band, X-band, R-band, and broad emission-line fluxes, we show that there are strong correlations between the broad-line flux and multi-wave bands involved with K-band, X-band and R-band flux. Simultaneously, we also considered the cor-relations of luminosity of the broad-line emission and the three different bands (K, X, R-band). After excluding the red-shift, the correlations between them are still relatively strong and the slopes of the linear regression are almost close to1, which are consistent with the theoretically predicted results. Moreover, the strong correlations of both luminosity and flux for broad-line emission and the other three bands suggest a close link between the formation of jets and accretion onto the central Kerr black hole, namely, the couple of the accretion disk and the jet of blazars. Here we found new experimental evidence that confirm theoretical speculations of Maraschi&Tavecchio. Moreover, we also found the relative location of BL Lacs and FSRQs are quite separated, and that the luminosity of the broad-line emission for BL Lacs is much less than one order magnitude for FSRQs. Furthermore, BL Lacs are always showing less correlation than FSRQs, and the two sub-samples (FSRQs and BL Lacs) in the X and R bands behave differently. So these results lead us to obtain that FSRqs and BL Lacs could be considered as a single population, or that FSRQs and BL Lacs should be regarded as a class. However they are in differ-ent evolutionary stages of blazars, and have different types of accretion disks with different line-to-continuum ratios. BL Lac objects are a subclass of blazars which have the low accretion rates. However FSRQs are an another subclass of blazars which have the high accretion rates. Our results seem to demonstrate the speculation of Cavaliere&D’Elia; Bottcher&Dermer, that FSRQs occur in the earlier, violent phase of the elliptical galaxy evolutionary sequence, which contains a significant amount of gas in the central region. These rich gases produced observed emission lines as well as violent radio and optical activity. When these gases are used up or expelled, the emission lines become very weak or disappear, and operation of the central engine becomes variable. In other words, a quasar evolves into a BL Lac object. |
PDF Full Text Request