jperkins@cfa.harvard.edu

¹ Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland
² Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
³ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
⁴ Department of Physics, Washington University, St. Louis, MO 63130, USA
⁵ Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA
⁶ Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA
⁷ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁹ Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA
¹⁰ School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
¹¹ School of Physics, National University of Ireland, Galway, Ireland
¹² Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA
¹³ Physics Department, McGill University, Montreal, QC H3A 2T8, Canada
¹⁴ Department of Physics, Purdue University, West Lafayette, IN 47907, USA
¹⁵ Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA
¹⁶ Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA
¹⁷ Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA
¹⁸ Physics Department, University of Utah, Salt Lake City, UT 84112, USA
¹⁹ NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771, USA
²⁰ Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau, France
²¹ Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA
²² Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
²³ Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA
²⁴ Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA
²⁵ Department of Physics, Pittsburg State University, 1701 South Broadway, Pittsburg, KS 66762, USA
²⁶ Department of Physics, Anderson University, 1100 East 5th Street, Anderson, IN 46012, USA
²⁷ European Southern Observatory, Karl-Schwarzchild-Strasse 2, 85748 Garching, Germany
²⁸ Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
²⁹ Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Ireland
³⁰ Now at Department of Physics, Durham University, South Road, Durham DH1 3LE, UK.
³¹ Author to whom any correspondence should be addressed.