Abstract
Theoretical implications of the recent OSSE observations of two AGNs with spectral breaks in soft γ‐rays, NGC 4151 and IC 4329a, are discussed. Two major classes of models, with either thermal or nonthermal electrons, are discussed. The purely nonthermal e± pair model is ruled out for NGC 4151. On the other hand, a nonthermal e± pair model with inefficient acceleration fits the NGC 4151 spectrum very well. Still, the simplest interpretation of the data for both objects is in terms of a plasma cloud with thermal electrons that Compton upscatter soft photons from the UV bump. The thermal plasma can form an active corona above the surface of an accretion disk and/or be pair dominated in IC 4329a, but neither is possible in the case of NGC 4151. Superposition of the contributions from AGNs similar to these two objects can fit the spectrum of the cosmic X‐ray background.
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