[1] CALTECH, Pasadena, CA 91125 USA
[2] Columbia Univ, Dept Astron, New York, NY 10027 USA
[3] NASA, Goddard Space Flight Ctr, Astron & Solar Phys Lab, Greenbelt, MD 20771 USA
[4] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[5] Johns Hopkins Univ, Ctr Astrophys Sci, Baltimore, MD 21218 USA
[6] Lab Astrophys Marseille, F-13376 Marseille, France
[7] Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA
[8] Yonsei Univ, Ctr Space Astrophy, Seoul 120749, South Korea
[9] Observ Carnegie Inst Washington, Pasadena, CA 91101 USA
[10] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA