1. Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UK
2. High-Energy Astrophysics Group, Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, D-85741 Garching, Germany
3. IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France
4. Department of Physics, University of Helsinki, PL 64 (Gustaf Hällströmin Katu 2), FI-D318, Helsinki, Finland
5. Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
6. Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802, USA