[1] Univ Tokyo, Res Ctr Early Universe, RESCUE, Bunkyo Ku, Tokyo 113, Japan
[2] Univ Tokyo, Dept Phys, Bunkyo Ku, Tokyo 113, Japan
[3] Max Planck Inst Extraterr Phys, D-85740 Garching, Germany
[4] Shanghai Jiao Tong Univ, Dept Appl Phys, Sch Sci, Inst Space & Astrophys, Shanghai 200030, Peoples R China