A Harmonic Analysis of the Large Scale Cosmic Ray Anisotropy

• Main Author: B E Kolterman
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: North Pole
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1087.8381; http://alpha.sinp.msu.ru/%7Epanov/Lib/Papers/CRANIS/Milagro-2008-icrc0722.pdf

Abstract: Here we present the results of a harmonic analysis of the large scale cosmic-ray anisotropy as observed by the Milagro observatory. The Milagro observatory is a water Cherenkov detector located in the Jemez mountains outside of Los Alamos, New Mexico. With a high duty cycle and large field-of-view, Milagro is an excellent instrument for measuring this anisotropy with high sensitivity at TeV energies. We show a two-dimensional map of the sidereal anisotropy generated by the fitting of three harmonics to separate declination bands taken from a six year data sample consisting of 150 billion events, the largest such data set in existence. We observe an anisotropy with a magnitude around 0.1% for cosmic rays with a median energy of 3 TeV. The dominant feature is a deficit region in the direction of the Galactic North Pole with a range in declination of -10 to 45 degrees and 150 to 225 degrees in right ascension. We also present results from an examination of the time evolution and the energy dependence of the anisotropy signal.