dgall@physics.purdue.edu cui@physics.purdue.edu

¹ Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA
² Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
³ Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA
⁴ Department of Physics, Washington University, St. Louis, MO 63130, USA
⁵ Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA
⁶ School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁸ School of Physics, University College Dublin, Belfield, Dublin 4, Republic of Ireland
⁹ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
¹⁰ School of Physics, National University of Ireland, Galway, Republic of Ireland
¹¹ Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA
¹² Physics Department, McGill University, Montreal, QC H3A 2T8, Canada
¹³ Physics Department, University of Utah, Salt Lake City, UT 84112, USA
¹⁴ Department of Physics, Purdue University, West Lafayette, IN 47907, USA
¹⁵ Department of Physics, Grinnell College, Grinnell, IA 50112-1690, USA
¹⁶ Department of Astronomy & Astrophysics, Pennsylvania State University, University Park, PA 16802, USA
¹⁷ Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA
¹⁸ Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau, France
¹⁹ Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA
²⁰ Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA
²¹ Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA
²² Department of Physics, Pittsburg State University, 1701 South Broadway, Pittsburg, KS 66762, USA
²³ Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
²⁴ Department of Physics, Anderson University, 1100 East 5th Street, Anderson, IN 46012, USA
²⁵ Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Republic of Ireland
²⁶ Instituto de Astronomia y Fisica del Espacio, Casilla de Correo 67 - Sucursal 28, (C1428ZAA) Ciudad Autnoma de Buenos Aires, Argentina
²⁷ Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
²⁸ Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Republic of Ireland
²⁹ Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA
³⁰ XMM-Newton-SOC, European Space Astronomy Centre, ESA, 28691 Villanueva de la Cañada (Madrid), Spain
³¹ ETH Zurich, CH-8093, Switzerland
³² INAF National Institute for Astrophysics, I-00136 Rome, Italy
³³ Universidad Complutense, E-28040 Madrid, Spain
³⁴ Technische Universität Dortmund, D-44221 Dortmund, Germany
³⁵ Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain
³⁶ Università di Padova and INFN, I-35131 Padova, Italy
³⁷ Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
³⁸ University of Łódź, PL-90236 Lodz, Poland
³⁹ Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, Germany
⁴⁰ Max-Planck-Institut für Physik, D-80805 München, Germany
⁴¹ Università di Siena, and INFN Pisa, I-53100 Siena, Italy
⁴² Universitat de Barcelona (ICC/IEEC), E-08028 Barcelona, Spain
⁴³ Universität Würzburg, D-97074 Würzburg, Germany
⁴⁴ IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain
⁴⁵ Depto. de Astrofisica, Universidad, E-38206 La Laguna, Tenerife, Spain
⁴⁶ Università di Udine, and INFN Trieste, I-33100 Udine, Italy
⁴⁷ Institut de Cienciès de l'Espai (IEEC-CSIC), E-08193 Bellaterra, Spain
⁴⁸ Inst. de Astrofísica de Andalucia (CSIC), E-18080 Granada, Spain
⁴⁹ University of California, Davis, CA-95616-8677, USA
⁵⁰ Tuorla Observatory, Turku University, FI-21500 Piikkiö, Finland
⁵¹ Institute for Nuclear Research and Nuclear Energy, BG-1784 Sofia, Bulgaria
⁵² INAF/Osservatorio Astronomico and INFN, I-34143 Trieste, Italy
⁵³ ICREA, E-08010 Barcelona, Spain
⁵⁴ Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy
⁵⁵ Authors to whom any correspondence should be addressed.
⁵⁶ Supported by INFN Padova.
⁵⁷ Deceased.