Preliminary analysis of two‐hemisphere observations of sidereal anisotropies of galactic cosmic rays

Abstract

By using the two‐hemisphere network of underground muon telescopes we have examined the average sidereal daily variations in the count rates recorded by 48‐component muon telescopes. The telescopes respond to primary cosmic rays with rigidities between ∼140 and 1700 GV and view almost the entire celestial sphere. We have modeled the data by using Gaussian functions, and we have related the Gaussian parameters to the recent tail‐in and loss cone anisotropy model proposed by Nagashima et al. [1995a, b] to explain the sidereal daily variations. We have used the model parameters to derive the rigidity and latitude spectra of the galactic anisotropies and find them to be qualitatively in agreement with Nagashima et al.'s predictions. The results indicate, however, that the tail‐in anisotropy is asymmetric about its reference axis, whereas the loss cone anisotropy is more symmetric. We show that these characteristics of the galactic anisotropies may explain the north–south asymmetry observed in the amplitude of the sidereal diurnal variation derived from Fourier analysis techniques.