OBSERVATION OF ANISOTROPY IN THE GALACTIC COSMIC-RAY ARRIVAL DIRECTIONS AT 400 TeV WITH ICECUBE

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 2009 May and 2010 May. The data include a total of 33 × 10⁹ muon events with a median angular resolution of ~3°. 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 sky map shows a different anisotropy structure including a deficit with a post-trial significance of –6.3σ. 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.

Description
Keywords
astroparticle physics, cosmic rays, neutrinos, MAGNETOHYDRODYNAMIC TURBULENCE, INTERSTELLAR-MEDIUM, MAGNETIC-FIELD, MILAGRO, DIFFUSION, ORIGIN, Astronomy & Astrophysics
Citation
Abbasi, R., et al. (2012): Observation of Anisotropy in the Galactic Cosmic-ray Arrival Directions at 400 TeV with IceCube. The Astrophysical Journal, 746(1). DOI: http://dx.doi.org/10.1088/0004-637X/746/1/33