A #nodel is presented which assumes the existence of cold dense clouds near the central engine of active galactic nuclei (AGNs). The effects of such clouds on the observed spectrum are explored. It is shown that this model is consistent with the complicated observed spectra and variability behavior of most extensively studied Seyfert nuclei. The results are compared with other proposed models. The existing observational evidence appears to support the "cloud-model."
Compact plasmas, which exist near black hole candidates and in gamma-ray burst sources, commonly exhibit self-organized nonlinear behavior. A model that simulates the nonlinear behavior of a compact radiative plasma is constructed directly from the observed luminosity and variability. The simulation shows that such a plasma self-organizes and that the degree of nonlinearity as well as the slope of the power density spectrum increases with compactness. The simulation is based on a cellular automaton table that includes the properties of the hot (relativistic) plasma and the magnitude of the energy perturbations. The plasma cools, or heats up, depending on whether it releases more or less energy than that of a single perturbation. The energy released depends on the plasma density and temperature and the energy of the perturbations. Strong perturbations may cool the previously heated plasma through shocks and/or pair creation. New observations of some active galactic nuclei and gamma-ray bursts are consistent with the simulation.
We explain why compact sources are nonlinear and investigate the nonlinearity of MCG-6-30-15. We argue that the central engine of this Seyfert nucleus is compact and show that it exhibits a specific nonlinear behavior similar to that of a system in a critically self-organized state.
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