1. Institute for Particle Physics and Astrophysics, ETH Zürich, Wolfgang-Pauli-Str. 27, CH-8093 Zürich, Switzerland
2. Institute for Astronomy, Oskar Klein Centre, Stockholm University, Roslagstullsbacken 21, SE-115 44 Stockholm, Sweden
3. School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
4. Dipartimento di Fisica ‘G. Occhialini’, Università degli Studi di Milano Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy
5. INAF-Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate, Italy
6. Modulos AG, Technoparkstrasse 1, CH-8005 Zürich, Switzerland
7. Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK