1. Centre Spatial de Liège, University of Liège, Belgium; Institut d'Astrophysique et de Géophysique, University of Liège, Belgium.
2. Max-Planck-Institut für Astrophysik, Garching, Germany.
3. Observatoire Royal de Belgique, Bruxelles, Belgium.
4. Department of Physics and Oskar Klein Center for Cosmoparticle Physics, University of Stockholm, Stockholm, Sweden.