The radial distribution of gamma rays and cosmic rays in the outer Galaxy
Abstract
The radial distribution of the high-energy (70 MeV-5 GeV) gamma-ray emissivity in the outer Milky Way is derived. The kinematics of HI are used to construct column-density maps in three galacto-centric distance ranges in the outer Galaxy. These maps are used in combination with COS-B gamma-ray data to determine gamma-ray emissivities in these distance ranges. A steep negative gradient of the emissivity for the 70 MeV-150 MeV energy range is found in the outer Galaxy. The emissivity for the 300 MeV-5 GeV range is found to be approximately constant (within ~20%) and equal to the local value out to large (~20 kpc) galacto-centric distances. These results imply a hardening of the gamma-ray spectrum with increrasing distance and for R > 16 kpc the spectrum is shown to be consistent with a π°-decay spectrum with the intensity expected from the local measurement of the cosmic-ray nuclei spectrum. The energy-dependent decrease is interpreted as a steep gradient in the cosmic-ray electron density and a near constancy of the nuclear component. The galactic origin of electrons with energies up to several hundreds of MeV is confirmed, while for cosmic-ray nuclei with energies of a few GeV either confinement in a large galactic halo or an extragalactic origin is suggested by the data.
- Publication:
-
Advances in Space Research
- Pub Date:
- 1984
- DOI:
- 10.1016/0273-1177(84)90067-X
- Bibcode:
- 1984AdSpR...3j..83H
- Keywords:
-
- Galactic Cosmic Rays;
- Gamma Rays;
- Radiation Distribution;
- Cos-B Satellite;
- Electron Distribution;
- Emissivity;
- Interstellar Matter;
- Milky Way Galaxy;
- Radial Distribution;
- Space Radiation;
- Cosmic rays;
- gamma rays;
- interstellar matter;
- COS-B