[1] European So Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany
[2] Univ Erlangen Nurnberg, Dr Karl Remeis Observ, D-96049 Bamberg, Germany
[3] Univ Erlangen Nurnberg, Erlangen Ctr Astroparticle Phys, Astron Inst, D-96049 Bamberg, Germany
[4] CALTECH, Space Radiat Lab, Pasadena, CA 91125 USA
[5] Radboud Univ Nijmegen, Dept Astrophys, Inst Math Astrophys & Particle Phys, NL-6500 GL Nijmegen, Netherlands
[6] Chinese Acad Sci, Yunnan Observ, Key Lab Struct & Evolut Celestial Objects, Kunming 650011, Peoples R China
[7] Univ Bonn, Argelander Inst Astron, D-53121 Bonn, Germany
[8] CALTECH, Div Phys Math & Astron, Pasadena, CA 91125 USA
[9] Max Planck Inst Astron, D-69117 Heidelberg, Germany
[10] Queens Univ Belfast, Sch Math & Phys, Astrophys Res Ctr, Belfast BT7 1NN, Antrim, North Ireland
[11] Univ Hawaii Manoa, Inst Astron, Honolulu, HI 96822 USA