[1] Fermilab Natl Accelerator Lab, Batavia, IL 60510 USA
[2] Univ Chicago, Dept Astron & Astrophys, Chicago, IL 60637 USA
[3] NYU, Dept Phys, New York, NY 10003 USA
[4] Ohio State Univ, Dept Astron, Columbus, OH 43210 USA
[5] Max Planck Inst Astrophys, D-85741 Garching, Germany
[6] Princeton Univ Observ, Princeton, NJ 08544 USA
[7] Univ Washington, Dept Astron, Seattle, WA 98195 USA
[8] Univ Chicago, Yerkes Observ, Williams Bay, WI 53191 USA
[9] Apache Point Observ, Sunspot, NM 88349 USA
[10] Univ Pittsburgh, Dept Phys & Astron, Pittsburgh, PA 15260 USA
[11] Eotvos Lorand Univ, Dept Phys, H-1518 Budapest, Hungary
[12] Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA
[13] Univ Tokyo, Sch Sci, Res Ctr Early Universe, Tokyo 1130033, Japan
[14] Univ Tokyo, Inst Astron, Tokyo 1130033, Japan
[15] Univ Arizona, Steward Observ, Tucson, AZ 85721 USA
[16] Univ Tokyo, Inst Cosm Ray Res, Kashiwa, Chiba 2778582, Japan
[17] USN Observ, Washington, DC 20392 USA
[18] USN, Res Lab, Remote Sensing Div, Washington, DC 20375 USA
[19] CERN, IT Div, CH-1211 Geneva 23, Switzerland
[20] Univ Chicago, Enrico Fermi Inst, Chicago, IL 60637 USA
[21] Univ Sussex, Sussex Astron Ctr, Brighton BN1 9QJ, E Sussex, England
[22] Univ Michigan, Dept Phys, Ann Arbor, MI 48109 USA
[23] Univ Edinburgh, Dept Phys & Astron, Edinburgh EH9 3JZ, Midlothian, Scotland
[24] CALTECH, Dept Astron, Pasadena, CA 91125 USA
[25] Carnegie Mellon Univ, Dept Phys, Pittsburgh, PA 15213 USA
[26] Penn State Univ, Dept Astron & Astrophys, University Pk, PA 16802 USA
[27] Univ Maryland, Dept Astron, College Pk, MD 20742 USA
[28] Univ Hawaii, Inst Astron, Honolulu, HI 96822 USA
[29] Univ Penn, Dept Phys, Philadelphia, PA 19101 USA
[30] Drexel Univ, Dept Phys, Philadelphia, PA 19104 USA