Observation of TeV–PeV cosmic ray anisotropy with IceCube, IceTop and AMANDA

Abstract

The study of cosmic ray anisotropy in the TeV–PeV energy range could provide clues about the origin and propagation of cosmic rays in our galactic neighborhood. Since the observed anisotropy is very small, below the per mille level, large event volumes are needed in order to characterize it in sufficient detail. The IceCube Observatory has already collected more than 150 billion cosmic ray induced muon events. This large data sample made it possible to detect anisotropies in the southern hemisphere, down to the 10−5 level, at primary energies in excess of 10TeV. The observed anisotropy is not a simple dipole, but it can be described as composed of multipole components of the spherical harmonic expansion, down to about 10°. A change in topological structure of the cosmic ray arrival distribution is observed above 100TeV. Data collected with the air shower array IceTop above 300TeV confirm the observations up to the PeV energy scale. Moreover, the addition of data collected with the AMANDA neutrino telescope, which operated between 2000 and 2007, has enabled us to search for time variability in the observed TeV anisotropy.