Abstract
Results are presented of a harmonic analysis of the large-scale cosmic-ray (CR) anisotropy as observed by the Milagro observatory. We show a two-dimensional display of the sidereal anisotropy projections in right ascension (R.A.) 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 CRs with a median energy of 6 TeV. The dominant feature is a deficit region of depth (2.49 ± 0.02 stat. ± 0.09 sys.) ×10-3 in the direction of the Galactic north pole centered at 189 deg R.A. We observe a steady increase in the magnitude of the signal over seven years.
Original language | English (US) |
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Pages (from-to) | 2121-2130 |
Number of pages | 10 |
Journal | Astrophysical Journal |
Volume | 68 |
Issue number | 2 |
DOIs | |
State | Published - Jun 2009 |
Keywords
- Cosmic rays
- Galaxy: halo
- ISM: magnetic fields
- Solar neighborhood
- Sun: activity
- Supernova remnants
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science