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Small-scale anisotropy of cosmic rays above 10^19eV observed with the Akeno Giant Air Shower Array

M. Takeda·N. Hayashida·K. Honda·N. Inoue·K. Kadota·F. Kakimoto·K. Kamata·S. Kawaguchi·Y. Kawasaki·N. Kawasumi·E. Kusano·Y. Matsubara·K. Murakami·M. Nagano·D. Nishikawa·H. Ohoka·S. Osone·N. Sakaki·M. Sasaki·K. Shinozaki·N. Souma·M. Teshima·R. Torii·I. Tsushima·Y. Uchihori·T. Yamamoto·S. Yoshida·H. Yoshii
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Abstract

With the Akeno Giant Air Shower Array (AGASA), 581 cosmic rays above 10^19eV, 47 above 4 x 10^19eV, and 7 above 10^20eV are observed until August 1998. Arrival direction distribution of these extremely high energy cosmic rays has been studied. While no significant large-scale anisotropy is found on the celestial sphere, some interesting clusters of cosmic rays are observed. Above 4 x 10^19eV, there are one triplet and three doublets within separation angle of 2.5^o and the probability of observing these clusters by a chance coincidence under an isotropic distribution is smaller than 1 %. Especially the triplet is observed against expected 0.05 events. The cos(θ_GC) distribution expected from the Dark Matter Halo model fits the data as well as an isotropic distribution above 2 x 10^19eV and 4 x 10^19eV, but is a poorer fit than isotropy above 10^19eV. Arrival direction distribution of seven 10^20eV cosmic rays is consistent with that of lower energy cosmic rays and is uniform. Three of seven are members of doublets above about 4 x 10^19eV.

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M. Takeda, N. Hayashida, K. Honda, N. Inoue, K. Kadota, F. Kakimoto, K. Kamata, S. Kawaguchi, Y. Kawasaki, N. Kawasumi, E. Kusano, Y. Matsubara, K. Murakami, M. Nagano, D. Nishikawa, H. Ohoka, S. Osone, N. Sakaki, M. Sasaki, K. Shinozaki, N. Souma, M. Teshima, R. Torii, I. Tsushima, Y. Uchihori, T. Yamamoto, S. Yoshida, H. Yoshii. 2000-06-21. Small-scale anisotropy of cosmic rays above 10^19eV observed with the Akeno Giant Air Shower Array. https://doi.org/10.1086/307646

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