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Discovery of Localized Regions of Excess 10-TeV Cosmic Rays

Phys. Rev. Lett. 101, 221101 – Published 24 November 2008
A. A. Abdo et al. (Milagro Collaboration)
Physics logo See Viewpoint: Puzzling hot spots in the cosmic-ray sky


The 7 year data set of the Milagro TeV observatory contains 2.2×1011 events of which most are due to hadronic cosmic rays. These data are searched for evidence of intermediate scale structure. Excess emission on angular scales of 10° has been found in two localized regions of unknown origin with greater than 12σ significance. Both regions are inconsistent with pure gamma-ray emission with high confidence. One of the regions has a different energy spectrum than the isotropic cosmic-ray flux at a level of 4.6σ, and it is consistent with hard spectrum protons with an exponential cutoff, with the most significant excess at 10TeV. Potential causes of these excesses are explored, but no compelling explanations are found.

DOI: http://dx.doi.org/10.1103/PhysRevLett.101.221101

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  • Received 23 January 2008
  • Revised 29 September 2008
  • Published 24 November 2008

© 2008 The American Physical Society


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Puzzling hot spots in the cosmic-ray sky

Published 24 November 2008

Unusual localized excess fluxes of cosmic rays of unknown origin have been observed at an energy of 10 TeV. Several explanations are being considered, but none are convincing.

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