The Galactic electron spectrum below 1000 MeV

Abstract

The local synchrotron emissivity spectrum is derived from radio observations in the anticentre direction, using absorption optical depths derived from the distribution of the diffuse H alpha radiation and statistical properties of radio galaxies at low frequencies. The corresponding electron spectrum, which relates largely to regions of the Galaxy of median distance some 600 pc away from the Sun, is deduced for the range 100 MeV-1 GeV and comparison is made with the 'local' spectrum (at the Sun) derived in a quite different way on the basis of the ratio of measured fluxes of electrons and positrons in the primary radiation. The gamma -ray data of the Cos-B experiment are analysed in terms of the respective contributions from electron bremsstrahlung and proton interactions and the ratio of the flux of electrons to protons is determined; this relates to the electron spectrum at distances from the Sun in the range 2-4 kpc.