Gamma-Ray Properties of Active Galactic Nuclei
Abstract
Recent observations by the Compton Observatory have increased our knowledge about the gamma-ray emission from Active Galactic Nuclei considerably. The three most important findings of CGRO with respect to AGNs are: first, no Seyfert 1 galaxy has been found to show emission above 500 keV. The by far strongest Seyfert 1 galaxy NGC 4151 shows a spectrum which falls off exponentially with an e-folding energy of 39 keV between 65 and 500 keV. OSSE so far has detected or has indications of detections for seven additional Seyfert 1 galaxies, which. however, all show very weak hard X-ray emission compared to NGC 4151. No annihilation feature has been seen from any Seyfert galaxy to this date. Second, the radio galaxy Cen A shows a power-law energy spectrum from hard X-ray energies of about 150 keV to at least 3 MeV. It has not been seen at EGRET-energies. Third. a new class of AGN was discovered at energies above 100 MeV by EGRET. The power of these objects in gamma-rays can dominate the luminosity in other spectral ranges. These objects are associated with extragalactic sources that have blazar properties. The high-energy gamma-ray emission is probably produced in relativistically outflowing jets. At hard X-ray energies the objects are rather weak. Spectral breaks at MeV energies were found by COMPTEL for three of these objects (3C 273, 3C 279, and PKS 0528+134).
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- June 1994
- DOI:
- 10.1086/192021
- Bibcode:
- 1994ApJS...92..593S
- Keywords:
-
- Active Galactic Nuclei;
- Gamma Ray Astronomy;
- Gamma Ray Spectra;
- Seyfert Galaxies;
- Spectral Emission;
- Blazars;
- Gamma Ray Observatory;
- Radio Galaxies;
- Astronomy;
- GALAXIES: ACTIVE;
- GALAXIES: NUCLEI;
- GALAXIES: SEYFERT;
- GAMMA RAYS: OBSERVATIONS