[1] Harvard Smithsonian Ctr Astrophys, Fred Lawrence Whipple Observ, Amado, AZ 85645 USA
[2] Columbia Univ, Dept Phys & Astron, Barnard Coll, New York, NY 10027 USA
[3] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA
[4] Univ Calif Santa Cruz, Santa Cruz Inst Particle Phys, Santa Cruz, CA 95064 USA
[5] Univ Calif Santa Cruz, Dept Phys, Santa Cruz, CA 95064 USA
[6] Washington Univ, Dept Phys, St Louis, MO 63130 USA
[7] Univ Leeds, Sch Phys & Astron, Leeds LS2 9JT, W Yorkshire, England
[8] Argonne Natl Lab, Argonne, IL 60439 USA
[9] Univ Coll Dublin, Sch Phys, Dublin 4, Ireland
[10] Natl Univ Ireland Galway, Sch Phys, Galway, Ireland
[11] Adler Planetarium & Astron Museum, Dept Astron, Chicago, IL 60605 USA
[12] Purdue Univ, Dept Phys, W Lafayette, IN 47907 USA
[13] Grinnell Coll, Dept Phys, Grinnell, IA 50112 USA
[14] Univ Utah, Dept Phys & Astron, Salt Lake City, UT 84112 USA
[15] McGill Univ, Dept Phys, Montreal, PQ H3A 2T8, Canada
[16] Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA
[17] Univ Delaware, Bartol Res Inst, Newark, DE 19716 USA
[18] Rutgers State Univ, Dept Phys & Astron, Piscataway, NJ 08854 USA
[19] Univ Chicago, Enrico Fermi Inst, Chicago, IL 60637 USA
[20] Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA
[21] Depauw Univ, Dept Phys & Astron, Greencastle, IN 46135 USA
[22] Iowa State Univ, Dept Phys & Astron, Ames, IA 50011 USA
[23] DESY, D-15738 Zeuthen, Germany
[24] Galway Mayo Inst Technol, Dept Life & Phys Sci, Galway, Ireland
[25] Univ Potsdam, Inst Phys & Astron, D-14476 Potsdam, Germany
[26] Cork Inst Technol, Dept Appl Phys & Instrumentat, Cork, Ireland
[27] Columbia Univ, Columbia Astrophys Lab, New York, NY 10027 USA
[28] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA