ealiu@bartol.udel.edu wakely@uchicago.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 Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
⁴ Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA
⁵ Physics Department, McGill University, Montreal, QC H3A 2T8, Canada
⁶ Department of Physics, Washington University, St. Louis, MO 63130, 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, Republic of Ireland
¹¹ School of Physics, National University of Ireland, Galway, Republic of Ireland
¹² Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA
¹³ Department of Physics, Purdue University, West Lafayette, IN 47907, USA
¹⁴ Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA
¹⁵ Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
¹⁶ Laboratoire Leprince-Ringuet, Ecole Polytechnique, CNRS/IN2P3, F-91128 Palaiseau, France
¹⁷ Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA
¹⁸ Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA
¹⁹ Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA
²⁰ Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA
²¹ Department of Physics, Pittsburg State University, 1701 South Broadway, Pittsburg, KS 66762, USA
²² Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
²³ Department of Physics, Anderson University, 1100 East 5th Street, Anderson, IN 46012, USA
²⁴ Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Republic of Ireland
²⁵ Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
²⁶ Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Republic of Ireland
²⁷ Address correspondence to E. Aliu () or S. P. Wakely ().