Pair Plasmas in the Central Engine of Active Galactic Nuclei

摘要

As the most promising model for the X-ray emission from a class of Active Galactic Nuclei (AGNs) represented by radio-quiet quasars and Seyfert nuclei, we introduce the non-thermal pair cascade model, where soft photons are Comptonized by non-thermal electron-positron pair plasmas produced by gamma-rays. After summarizing the simplest model of this kind, the 'homogeneous spherical cascade model', our most recent work on the 'surface cascade model' is presented, where a geometrical effect is introduced. Many characteristics of this model are qualitatively similar to the homogeneous cascade model. However, an important difference is that gamma-ray depletion is much more efficient in the surface cascade, and consequently this model naturally satisfies the severe observational constraint imposed by the gamma-ray background radiation.