[1] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[2] Univ Calif Berkeley, Lawrence Berkeley Lab, Div Phys, Berkeley, CA 94720 USA
[3] Univ Calif Berkeley, Ctr Particle Astrophys, Berkeley, CA 94720 USA
[4] Queen Mary Univ London, London E1 4NS, England
[5] Univ Roma Tor Vergata, Dipartimento Fis, I-00133 Rome, Italy
[6] CALTECH, Jet Prop Lab, Pasadena, CA 91109 USA
[7] CALTECH, Pasadena, CA 91125 USA
[8] Univ Calif Berkeley, Lawrence Berkeley Lab, Natl Energy Res Sci Comp Ctr, Berkeley, CA 94720 USA
[9] CNR, IROE, I-50127 Florence, Italy
[10] Univ Roma La Sapienza, Dipartimento Fis, I-00185 Rome, Italy
[11] Univ Oxford, Dept Astrophys, Oxford OX1 3RH, England
[12] Inst Super Tecn, CENTRA, P-1096 Lisbon, Portugal
[13] Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA
[14] Cardiff Univ, Dept Phys & Astron, Cardiff CF2 3YB, S Glam, Wales
[15] Univ Toronto, Dept Phys & Astron, Toronto, ON M5S 1A1, Canada
[16] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[17] Copernicus Astron Ctr, PL-00716 Warsaw, Poland
[18] Univ Calif Berkeley, Dept Astron, Berkeley, CA 94720 USA