Observation of Anisotropy in the Galactic Cosmic Ray Arrival Directions at 400 Tev with Icecube

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 33×10 muon events with a median angular resolution of ∼ 3◦ 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 -6.3σ. 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. Subject headings: cosmic rays — anisotropy 1 Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA 2 Dept. of Physics and Astronomy, University of Gent, B-9000 Gent, Belgium 3 Dept. of Physics, University of Wisconsin, River Falls, WI 54022, USA 4 DESY, D-15735 Zeuthen, Germany 5 Dept. of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand 6 Dept. of Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK 7 Dept. of Physics, Pennsylvania State University, University Park, PA 16802, USA 8 III. Physikalisches Institut, RWTH Aachen University, D52056 Aachen, Germany 9 now at Dept. of Physics and Astronomy, Rutgers University, 2 IceCube Collaboration: Abbasi et al.