1. Institute of Physics, Laboratory of Astrophysics , École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix , Switzerland
2. Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, CA 94720 , USA
3. Department of Astronomy, Tsinghua University , Beijing 100084 , China
4. Kavli Institute for Particle Astrophysics and Cosmology, Stanford University , 452 Lomita Mall, Stanford, CA 94305 , USA
5. Instituto de Astrofísica de Canarias , s/n, E-38205 La Laguna, Tenerife , Spain
6. Departamento de Astrofísica, Universidad de La Laguna , E-38206 La Laguna, Tenerife , Spain
7. Aix Marseille Université , CNRS, CNES, LAM, F-13388 Marseille , France
8. CPPM, Aix-Marseille Université , CNRS/IN2P3, CPPM UMR 7346, F-13288 Marseille , France
9. Tsinghua Center for Astrophysics, Department of Astronomy, Tsinghua University , Beijing 100084 , P.R. China