Galactic centre gamma-rays from trapped cosmic rays

The emissivity of Galactic-Center (GC) gamma-rays with energies greater than 100 MeV is calculated by assuming that primary cosmic-ray nuclei lose all their energy before escaping from the Galaxy. A lower limit is derived for the cosmic-ray injection-rate ratio between the GC and the local region, and a general expression for gamma-ray emissivity from neutral-pion decay is obtained for cosmic rays that have the local injection spectrum and lose all their energy before Galactic escape. An upper limit to the Galactic magnetic field is determined from an analysis of radio synchrotron data for the region within about 2 deg of the Galactic Center. The results indicate that the GC gamma-ray flux above 100 MeV is consistent with a primary-cosmic-ray injection rate that is at least 100 times the local value. This is taken as additional evidence for a Galactic origin of low-energy cosmic rays.