The distribution of cosmic rays in the galaxy and their dynamics as deduced from recent γ-ray observations

Recent data from SAS-2 on the galactic y-ray line flux as a function of longitude reveal a broad maximum in the y-ray intensity in the region 11 < 30. These data, when unfolded, imply that the low-energy (1-10 GeY) galactic cosmic-ray flux varies with galactocentric distance and is about an order of magnitude higher than the local value in a toroidal region between 4 and 5 kpc from the galactic center. We further show that this enhancement can be plausibly accounted for by first-order Fermi acceleration, compression, and trapping of cosmic rays consistent with present ideas of galactic dynamics and galactic structure theory. Our calculations indicate that cosmic rays in the 4-5 kpc region are trapped and accelerated over a mean time of the order of a few million years or about 2-4 times the assumed trapping time in the solar region of the Galaxy. Cosmic-ray nucleons, cosmic-ray electrons, and ionized hydrogen gas are found to have a strikingly similar distribution in the Galaxy according to both the observational data and the theoretical model discussed here. Subject headings: cosmic rays galactic structure gamma rays