[1] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[2] Natl Inst Nat Sci, Natl Astron Observ Japan, Mitaka, Tokyo 1818588, Japan
[3] EO Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA
[4] Stockholm Univ, Dept Phys, Albanova Univ Ctr, S-10691 Stockholm, Sweden
[5] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[6] Hamilton Coll, Dept Phys, Clinton, NY 13323 USA
[7] Univ Utah, Dept Phys & Astron, Salt Lake City, UT 84112 USA
[8] Univ Tokyo, Grad Sch Sci, Inst Astron, Tokyo 1810015, Japan
[9] Univ Calif Santa Cruz, Santa Cruz Inst Particle Phys, Santa Cruz, CA 95064 USA
[10] Space Telescope Sci Inst, Baltimore, MD 21218 USA
[11] Univ Chicago, Dept Astron & Astrophys, Chicago, IL 60637 USA
[12] Univ Calif Davis, Dept Phys, Davis, CA 95616 USA
[13] Humboldt Univ, Inst Phys, D-12489 Berlin, Germany
[14] Univ Tokyo, Inst Cosm Ray Res, Chiba 2778582, Japan
[15] Oskar Klein Ctr, S-10691 Stockholm, Sweden
[16] CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA