The Extragalactic X-Ray and Gamma-Ray Backgrounds
Abstract
The review encompasses issues concerning the origin of the extragalactic X-ray background (XRB) and emphasizes the variety of existing models. A reference energy of 2 keV is employed to examine the estimated contributions from extragalactic discrete sources. The contributions are considered of a hot diffuse intergalactic gas and related low-luminosity AGNs, but the AGNs are considered to have X-ray spectra that do not match those of the 2-keV XRB very closely. Several models based on this finding are examined in which new classes of sources and novel mechanisms have been hypothesized. A unified scheme of AGNs is explained which accounts for the most of the XRB intensity independently of the observed spectral differences. It is concluded that deeper observations are needed to constrain the possible interpretations of the astrophysical and cosmological significance of the extragalactic XRB.
- Publication:
-
The Galactic and Extragalactic Background Radiation
- Pub Date:
- 1990
- Bibcode:
- 1990IAUS..139..345S
- Keywords:
-
- Background Radiation;
- Extraterrestrial Radiation;
- Gamma Ray Astronomy;
- Radiation Sources;
- X Ray Astronomy;
- Astronomical Models;
- Intergalactic Media;
- Quasars;
- Seyfert Galaxies;
- Astrophysics