@article{oai:repo.qst.go.jp:00042993,
 author = {Shinozaki, Kenji and Chikawa, Michiyuki and Fukushima, Masaki and Hayashida, Naoaki and Inoue, Naoya and Honda, Ken and Kadota, Kenji and Kakimoto, Fumio and Kamata, Kouichi and Kawaguchi, Setsuo and Kawakami, Saburo and Kawasaki, Yoshiya and Kawasumi, Norio and Mahrous, A and Mase, Keiichi and Mizobuchi, Tomoko and Morizane, Yuichirou and Nagano, Motohiko and Ohoka, Hideyuki and Osone, Satoko and Sakaki, Naoto and Sakurai, Nobuyuki and Sasaki, Makoto and Sasano, Masahiko and Takeda, Masahiro and Teshima, Masahiro and Tsushima, Itsurou and Torii, Reiko and Uchihori, Yukio and Vazquez, R and Yamamoto, Tokonatsu and Yoshida, Shigeru and Yoshii, Hisashi and 川崎 賀也 and 榊 直人 and 内堀 幸夫},
 journal = {The Astrophysical Journal},
 month = {Jun},
 note = {The origin of the highest energy cosmic rays (−1020 eV) is not well understood. Interesting models called ＾top-down￣ scenarios have been proposed to explain the origin. The g-ray flux in ultra?high-energy cosmic rays is a key parameter for giving constraints on such models. To study the properties of g-ray showers, we carry out simulation studies that take into account both the Landau-Pomeranchuk-Migdal effect and electromagnetic interactions in the geomagnetic field. Based on an analysis of muons in air showers observed by the Akeno Giant Air Shower Array, the upper limits on the g-ray flux are estimated to be 28% above 1019 eV and 67% above
1019.5 eV in the observed air showers at a confidence level of 95%. Above 1020 eV, the primary composition is in agreement with an extrapolation from lower energies, and there is no indication that the observed events are mostly g-ray showers. These results provide observational constraints for origin models up to the highest energies.},
 pages = {L117--L120},
 title = {UPPER LIMIT ON GAMMA-RAY FLUX ABOVE 1019 eV ESTIMATED BY THE AKENO GIANT AIR SHOWER ARRAY EXPERIMENT},
 volume = {57},
 year = {2002}
}