Soft γ-ray emission from the region of MCG8 -11 -11
Abstract
The galaxy MCG8 -11 -11 inside the 0.093 square degrees error-box of the X-ray source 2A0551 + 466 (ref. 1), was recently found to be a Type 1 Seyfert galaxy2. A 40-arcs error-box from the A3 experiment on HEAO1 has confined the X-ray emission to the nucleus or bar of this 14-mv galaxy3. The redshift is z = 0.0205 (ref. 2), corresponding to a distance of 123 Mpc (H0 = 50 km s-1 Mpc-1). The 2-10 keV luminosity ranges from 5 × 1043erg s-1 to 1.2 × 1044erg s-1 (refs 1,3). Hard X-ray emission above 20 keV from the region of MCG8 -11 -11 has been recently reported4, and the A2 experiment on HEAO 1 has provided for the first time the emission spectrum of this object up to 30 keV (ref. 5). During a balloon flight on 30 September 1979 from Palestine, Texas of the Milan/Southampton (MISO) low-energy γ-ray telescope, an excess at the 3.9σ level in the flux above 90 keV was detected from a region of the sky containing MCG8 -11 -11. The emission spectrum, evaluated in the energy range 0.02-19 MeV, has similar spectral characteristics to those observed with the same telescope and associated with the Seyfert galaxy NGC4151 (ref. 6). Both spectra show evidence for a high-energy cutoff close to 3 MeV and this feature could be interpreted on the basis of the `Penrose-Compton scattering' process7. A large amount of the observed low-energy γ-ray diffuse background8 could be produced by a few per cent of the X-ray emitting Seyfert galaxies having a γ-ray luminosity comparable with that observed from the region of NGC4151 or MCG8 -11 -11.
- Publication:
-
Nature
- Pub Date:
- July 1981
- DOI:
- 10.1038/292133a0
- Bibcode:
- 1981Natur.292..133P
- Keywords:
-
- Emission Spectra;
- Galactic Radiation;
- Gamma Ray Astronomy;
- Gamma Ray Spectra;
- Seyfert Galaxies;
- Active Galactic Nuclei;
- Background Radiation;
- Balloon-Borne Instruments;
- Gamma Ray Bursts;
- Gamma Ray Telescopes;
- Stochastic Processes;
- Astronomy