Galactic cosmic rays above 1018eV

Abstract

A study of the anisotropy of cosmic rays is presented and evidence is found for an enhancement of particles from the general direction of the galactic plane. Previous work in this field was concerned largely with data from extensive-air-shower detectors in the northern hemisphere and was interpreted in terms of an excess of particles from the south, namely a Galactic gradient. The authors show that a galactic-plane enhancement gives an equally good explanation of these results but when combined with southern hemisphere observations from the Chacaltaya array (Anda et al., 1981) and Sydney (Horton et al., 1983) the evidence favours galactic-plane enhancement rather strongly. The argument is strengthened by a detailed analysis of the amplitudes and phases of the harmonics from all the available experiments. At energies above several times 10¹⁹ eV the model fails and here the authors can see no objection to the commonly advanced idea of a preponderance of extragalactic particles.