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

TL;DR

This paper reports the detection of small-scale anisotropies in cosmic ray arrival directions in the TeV-PeV range using large datasets from IceCube, IceTop, and AMANDA, revealing complex structures and energy-dependent changes.

Contribution

It presents the first detailed characterization of cosmic ray anisotropy at TeV-PeV energies in the southern hemisphere using a combined large dataset from IceCube, IceTop, and AMANDA.

Findings

Anisotropy detected at the 10^-5 level in the southern hemisphere.

Complex multipole structure of cosmic ray arrival directions.

Change in anisotropy topology observed above 100 TeV.

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. Because the observed anisotropy is very small, below the per-mille level, large event volumes are needed in order to characterize it in sufficient detail. Over the last six years, the IceCube Observatory has collected 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 10 TeV. The observed anisotropy is not a simple dipole, but it can be described as composed of multipole components of the spherical harmonic expansion, to about 10$^{\circ}$. A change in topological structure of the cosmic ray arrival distribution is observed above 100 TeV. Data collected with the air shower array IceTop above 300 TeV 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.