Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff

  title={Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff},
  author={Masahiro Takeda and N. Hayashida and Ken Honda and Naoko Inoue and K. Kadota and Fumio Kakimoto and Keigo Kamata and S. Kawaguchi and Yoshiya Kawasaki and Norio Kawasumi and Hidemitsu Kitamura and E. Kusano and Yutaka Matsubara and Kazuaki Murakami and Motohiko Nagano and D. Nishikawa and Hideyuki Ohoka and N. Sakaki and Makoto Sasaki and Kenji Shinozaki and N. Souma and Masahiro Teshima and Rodney H. Torii and Itsuro Tsushima and Yukio Uchihori and T. Yamamoto and Shigeru Yoshida and Hisashi Yoshii},
  journal={Physical Review Letters},
The cosmic-ray energy spectrum above 10^{18.5} eV is reported using the updated data set of the Akeno Giant Air Shower Array (AGASA) from February 1990 to October 1997. The energy spectrum extends beyond 10^{20} eV and the energy gap between the highest energy event and the others is being filled up with recently observed events. The spectral shape suggests the absence of the 2.7 K cutoff in the energy spectrum or a possible presence of a new component beyond the 2.7 K cutoff. 

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