Origin of cosmic rays: Galactic models with halo

Abstract

Many years ago physical and radio-astronomical arguments and data led to the assumption that cosmic rays in the Galaxy (and probably in other galaxies) fill a more or less extended halo, but are not concentrated in the disk. It was not so long ago, however, that the existence of a radio-halo was discovered, in which the effective dimensions increase with a decrease in frequency. The frequency decrease occurs when relativistic electrons diffuse from the disk, losing energy due to bremsstrahlung and Compton scattering.

Meanwhile, some ambiguity on the question of the existence of a radio-halo, and other reasons, have led to a rather wide use of disk models, particularly those in which cosmic rays are present in the Galaxy only for a periodT _cr,d≲3×10⁶ yr. The authors have repeatedly stated the inadmissibility of such models and, generally, a homogeneous (leaky box) model for the origin of cosmic rays. The new data concerning the amount of radioactive¹⁰Be nuclei in cosmic rays near the Earth in no way contradict the halo models in which the lifetime of cosmic rays isT _cr,h∼10⁸ yr. In connection with the continuing controversy, the present paper is devoted to a detailed consideration of the difference between the homogeneous and diffusion models. Within the latter models some calculations on the chemical composition of cosmic rays have been carried out, which concern not only stable but also radioactive isotopes.