Evolution of the cosmic-ray anisotropy above 1014 eV

Abstract

The amplitude and phase of the cosmic-ray anisotropy are well established experimentally between 1011 eV and 1014 eV. The study of their evolution in the energy region 1014-1016 eV can provide a significant tool for the understanding of the steepening ("knee") of the primary spectrum. In this Letter, we extend the EAS-TOP measurement performed at E 0 1014 eV to higher energies by using the full data set (eight years of data taking). Results derived at about 1014 and 4 × 1014 eV are compared and discussed. Hints of increasing amplitude and change of phase above 10 14 eV are reported. The significance of the observation for the understanding of cosmic-ray propagation is discussed. © 2009. The American Astronomical Society. All rights reserved..