Electron-Positron Pairs, Compton Reflection, and the X-Ray Spectra of Active Galactic Nuclei
Abstract
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 < 10^6^ 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 α_x_ ~ 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 α_x_ ~ 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1990
- DOI:
- 10.1086/185851
- Bibcode:
- 1990ApJ...363L...1Z
- Keywords:
-
- Active Galactic Nuclei;
- Compton Effect;
- Electron-Positron Pairs;
- X Ray Spectra;
- Accretion Disks;
- Astronomical Spectroscopy;
- Background Radiation;
- Gamma Ray Spectra;
- Astrophysics;
- GALAXIES: NUCLEI;
- RADIATION MECHANISMS;
- X-RAYS: SPECTRA