Electron-positron pairs, Compton reflection, and the X-ray spectra of active galactic nuclei

Recent X-ray observations by the Japanese satellite Ginga have given new insight into the X-ray emission from active galactic nuclei (AGN). In particular, they have shown the importance of a spectral component reflected from cold, optically thick material (T < 10⁶^ K) very close to the central engine in these objects. Here we show that this result revives models in which much of the luminosity generated in X- and γ-ray energy bands in AGN is reprocessed via electron-positron pairs. In those models, nonthermal electron-positron pair injection in a compact region results in X-ray spectra with an energy spectral index of αₓ_ ~ 1. We show that if a substantial fraction of this radiation is incident upon cold material, the reflected component results in a composite spectrum with an average spectral index of αₓ_ ~ 0. 7 in the 1-30 keV energy range for a wide range of initial assumptions. Furthermore, our predicted spectra steepen above ~ 1 MeV and exhibit soft excesses below ~ 0. 5 keV. Such spectra agree well with the X-ray and γ-ray observations of AGN and the constraints imposed by the cosmic γ-ray background.