[1] Univ Texas Austin, Texas Cosmol Ctr, Austin, TX 78712 USA
[2] Univ Texas Austin, Dept Astron, Austin, TX 78712 USA
[3] Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA
[4] Univ Oxford, Oxford OX1 3RH, England
[5] Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA
[6] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[7] Princeton Univ, Dept Phys, Princeton, NJ 08544 USA
[8] Univ Toronto, Canadian Inst Theoret Astrophys, Toronto, ON M5S 3H8, Canada
[9] Princeton Univ, Princeton Ctr Theoret Phys, Princeton, NJ 08544 USA
[10] Univ British Columbia, Dept Phys & Astron, Vancouver, BC V6T 1Z1, Canada
[11] ADNET Syst Inc, Lanham, MD 20706 USA
[12] Columbia Univ, Columbia Astrophys Lab, New York, NY 10027 USA
[13] Univ Chicago, Dept Phys & Astrophys, KICP, Chicago, IL 60637 USA
[14] Univ Chicago, EFI, Chicago, IL 60637 USA
[15] Brown Univ, Dept Phys, Providence, RI 02912 USA
[16] UCLA Phys & Astron, Los Angeles, CA 90095 USA