Study of small-scale anisotropy of ultra-high-energy cosmic rays observed in stereo by the high resolution fly's eye detector

R. U. Abbasi, T. Abu-Zayyad, J. F. Amann, G. Archbold, R. Atkins, J. A. Bellido, K. Belov, J. W. Belz, S. BenZvi, D. R. Bergman, J. H. Boyer, G. W. Burt, Z. Cao, R. W. Clay, B. M. Connolly, B. R. Dawson, W. Deng, Y. Fedorova, J. Findlay, C. B. FinleyW. F. Hanlon, C. M. Hoffman, M. H. Holzscheiter, G. A. Hughes, P. Hüntemeyer, C. C.H. Jui, K. Klm, M. A. Kirn, B. C. Knapp, E. C. Loh, M. M. Maestas, N. Manago, E. J. Mannel, L. J. Marek, K. Martens, J. A.J. Matthews, J. N. Matthews, A. O'Neill, C. A. Painter, L. Perera, K. Reil, R. Riehle, M. D. Roberts, M. Sasaki, S. R. Schnetzer, M. Seman, K. M. Simpson, G. Sinnis, J. D. Smith, R. Snow, P. Sokolsky, C. Song, R. W. Springer, B. T. Stokes, J. R. Thomas, S. B. Thomas, G. B. Thomson, D. Tupa, S. Westerhoff, L. R. Wiencke, A. Zech

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90 Scopus citations


The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence detector which, operating in stereo mode, has a typical angular resolution of 0°.6 and is sensitive to cosmic rays with energies above 1018 eV. The HiRes cosmic-ray detector is thus an excellent instrument for the study of the arrival directions of ultra-high-energy cosmic rays. We present the results of a search for anisotropies in the distribution of arrival directions on small scales (<5°) and at the highest energies (>1019 eV). The search is based on data recorded between 1999 December and 2004 January, with a total of 271 events above 1019 eV. No small-scale anisotropy is found, and the strongest clustering found in the HiRes stereo data is consistent at the 52% level with the null hypothesis of isotropically distributed arrival directions.

Original languageEnglish (US)
Pages (from-to)L73-L76
JournalAstrophysical Journal
Issue number2 II
StatePublished - Aug 1 2004

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Acceleration of particles
  • Cosmic rays
  • Large-scale structure of universe

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