Journal
ASTROPHYSICAL JOURNAL
Volume 740, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/740/1/16
Keywords
astroparticle physics; cosmic rays
Categories
Funding
- U. S National Science Foundation-Office of Polar Programs
- U. S National Science Foundation-Physics Division
- University of Wisconsin Alumni Research Foundation
- Grid Laboratory Of Wisconsin (GLOW) at the University of Wisconsin-Madison
- Open Science Grid (OSG) grid infrastructure
- U. S Department of Energy
- National Energy Research Scientific Computing Center
- Louisiana Optical Network Initiative (LONI) grid computing resources
- National Science and Engineering Research Council of Canada
- Swedish Research Council
- Swedish Polar Research Secretariat
- Swedish National Infrastructure for Computing (SNIC)
- Knut and Alice Wallenberg Foundation, Sweden
- German Ministry for Education and Research (BMBF)
- Deutsche Forschungsgemeinschaft (DFG)
- Research Department of Plasmas with Complex Interactions (Bochum), Germany
- Fund for Scientific Research (FNRS-FWO)
- FWO Odysseus programme
- Flanders Institute to encourage scientific and technological research in industry (IWT)
- Belgian Federal Science Policy Office (Belspo)
- University of Oxford, United Kingdom
- Marsden Fund, New Zealand
- Japan Society for Promotion of Science (JSPS)
- Swiss National Science Foundation (SNSF), Switzerland
- EU
- Capes Foundation, Ministry of Education of Brazi
- Division Of Physics
- Direct For Mathematical & Physical Scien [757155] Funding Source: National Science Foundation
- STFC [ST/J000507/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/J000507/1] Funding Source: researchfish
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Between 2009 May and 2010 May, the IceCube neutrino detector at the South Pole recorded 32 billion muons generated in air showers produced by cosmic rays with a median energy of 20 TeV. With a data set of this size, it is possible to probe the southern sky for per-mil anisotropy on all angular scales in the arrival direction distribution of cosmic rays. Applying a power spectrum analysis to the relative intensity map of the cosmic ray flux in the southern hemisphere, we show that the arrival direction distribution is not isotropic, but shows significant structure on several angular scales. In addition to previously reported large-scale structure in the form of a strong dipole and quadrupole, the data show small-scale structure on scales between 15 degrees and 30 degrees. The skymap exhibits several localized regions of significant excess and deficit in cosmic ray intensity. The relative intensity of the smaller-scale structures is about a factor of five weaker than that of the dipole and quadrupole structure. The most significant structure, an excess localized at (right ascension alpha = 122 degrees.4 and declination d = -47 degrees.4), extends over at least 20 degrees in right ascension and has a post-trials significance of 5.3 sigma. The origin of this anisotropy is still unknown.
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