Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 x 10¹⁸ eV

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Amer Assoc Advancement Science
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Cosmic rays are atomic nuclei arriving from outer space that reach the highest energies observed in nature. Clues to their origin come from studying the distribution of their arrival directions. Using 3 x 10⁴ cosmic rays with energies above 8 x 10¹⁸ electron volts, recorded with the Pierre Auger Observatory from a total exposure of 76,800 km(2) sr year, we determined the existence of anisotropy in arrival directions. The anisotropy, detected at more than a 5.2σ level of significance, can be described by a dipole with an amplitude of (6.5)_(-0.9)^(+1.3) % toward right ascension α_(d) = 100 ± 10 degrees and declination δ_(d) = -24_(-13)(+12) degrees. That direction indicates an extragalactic origin for these ultrahighenergy particles.
© Amer Assoc Advancement Science. The successful installation, commissioning, and operation of the Pierre Auger Observatory would not have been possible without the strong commitment from the technical and administrative staff in Malargue, and the financial support from a number of funding agencies in the participat-ing countries. The full acknowledgments are in the Supplementary Materials. The Pierre Auger Collaboration will make public the data reproduced in the Figures of this paper on the Auger website on the link to this publication: Artículo firmao por mas de diez autores. Autoria conjunta: The Pierre Auger Collaboration