1. THE LARGE-SCALE COSMIC-RAY ANISOTROPY AS OBSERVED WITH MILAGRO
- Author
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C. P. Lansdell, James M. Ryan, B. E. Kolterman, D. Noyes, T. Aune, Brenda Dingus, David Berley, Peter Nemethy, J. T. Linnemann, C. M. Hoffman, G. W. Sullivan, B. T. Allen, R. W. Ellsworth, J. A. Goodman, R. Fleysher, P. H. Hüntemeyer, A. L. Shoup, A. J. Smith, M. M. Gonzalez, L. Fleysher, Allen Mincer, Sabrina Casanova, David A. Williams, A. A. Abdo, V. Vasileiou, B. Hopper, Julie McEnery, P. M. Saz Parkinson, G. P. Walker, Chang-Hsiao Chen, G. B. Yodh, J. Pretz, and G. Sinnis
- Subjects
Physics ,010308 nuclear & particles physics ,Cherenkov detector ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics (astro-ph) ,Astrophysics::Instrumentation and Methods for Astrophysics ,FOS: Physical sciences ,Astronomy and Astrophysics ,Cosmic ray ,Astrophysics ,01 natural sciences ,Declination ,law.invention ,Space and Planetary Science ,Observatory ,law ,Sidereal time ,0103 physical sciences ,Milagro ,Anisotropy ,Right ascension ,010303 astronomy & astrophysics - 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., Comment: 36 pages, 16 figures, submitted to ApJ
- Published
- 2009