1. Department of Physics, Tokyo Metropolitan University , 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397 , Japan
2. Department of Physics, Rikkyo University , 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501 , Japan
3. Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065 , Japan
4. National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588 , Japan
5. Institute for Cosmic Ray Research, The University of Tokyo , 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 , Japan
6. Graduate School of Science and Engineering, Saitama University , 255 Shimo-Okubo, Sakura, Saitama, Saitama 338-8570 , Japan
7. Faculty of Education, Shizuoka University , 836 Ohya, Suruga-ku, Shizuoka, Shizuoka 422-8529 , Japan
8. Netherlands Institute for Space Research (SRON) , Sorbonnelaan 2, 3584 CA Utrecht , the Netherlands
9. Department of Physics and Oskar Klein Center, Stockholm University , 106 91 Stockholm , Sweden