The Large Scale Cosmic-Ray Anisotropy as Observed with Milagro
Abstract
Results are presented of a harmonic analysis of the large scale cosmic-ray anisotropy as observed by the Milagro observatory. We show a two-dimensional display of the sidereal anisotropy pro jections in right ascension generated by the fitting of three harmonics to 18 separate declination bands. The Milagro observatory is a water Cherenkov detector located in the Jemez mountains near 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. The analysis is conducted using a seven year data sample consisting of more than 95 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 6 TeV. The dominant feature is a deficit region of depth (2.49 +/- 0.02 stat. +/- 0.09 sys.)x10^(-3) in the direction of the Galactic North Pole centered at 189 degrees right ascension. We observe a steady increase in the magnitude of the signal over seven years.
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Cite
@article{arxiv.0806.2293,
title = {The Large Scale Cosmic-Ray Anisotropy as Observed with Milagro},
author = {A. A. Abdo and B. T. Allen and T. Aune and D. Berley and S. Casanova and C. Chen and B. L. Dingus and R. W. Ellsworth and L. Fleysher and R. Fleysher and M. M. Gonzalez and J. A. Goodman and C. M. Hoffman and B. Hopper and P. H. Hüntemeyer and B. E. Kolterman and C. P. Lansdell and J. T. Linnemann and J. E. McEnery and A. I. Mincer and P. Nemethy and D. Noyes and J. Pretz and J. M. Ryan and P. M. Saz Parkinson and A. Shoup and G. Sinnis and A. J. Smith and G. W. Sullivan and V. Vasileiou and G. P. Walker and D. A. Williams and G. B. Yodh},
journal= {arXiv preprint arXiv:0806.2293},
year = {2009}
}
Comments
36 pages, 16 figures, submitted to ApJ