Observation of an Anisotropy in the Galactic Cosmic Ray arrival direction at 400 TeV with IceCube

TL;DR

This study reports the first observation of energy-dependent anisotropy in Galactic cosmic ray arrival directions at 400 TeV using IceCube data, revealing a new anisotropy feature at high energies.

Contribution

It presents the first measurement of energy-dependent cosmic ray anisotropy in the Southern Hemisphere up to 400 TeV using IceCube muon data.

Findings

Anisotropy at 20 TeV differs from that at 400 TeV.

A new anisotropy feature with a significant deficit at 400 TeV.

Energy dependence of cosmic ray anisotropy observed.

Abstract

In this paper we report the first observation in the Southern hemisphere of an energy dependence in the Galactic cosmic ray anisotropy up to a few hundred TeV. This measurement was performed using cosmic ray induced muons recorded by the partially deployed IceCube observatory between May 2009 and May 2010. The data include a total of 33$\times 10^{9}$ muon events with a median angular resolution of $\sim3^{\circ}$ degrees. A sky map of the relative intensity in arrival direction over the Southern celestial sky is presented for cosmic ray median energies of 20 and 400 TeV. The same large-scale anisotropy observed at median energies around 20 TeV is not present at 400 TeV. Instead, the high energy skymap shows a different anisotropy structure including a deficit with a post-trial significance of -6.3$\sigma$. This anisotropy reveals a new feature of the Galactic cosmic ray distribution, which must be incorporated into theories of the origin and propagation of cosmic rays.