[1] Chinese Acad Sci, Inst High Energy Phys, Key Lab Particle Astrophys, Beijing 100049, Peoples R China
[2] Univ Chinese Acad Sci, Chinese Acad Sci, Beijing 100049, Peoples R China
[3] Eberhard Karls Univ Tubingen, Kepler Ctr Astro & Particle Phys, Inst Astron & Astrophys, D-72076 Tubingen, Germany
[4] Beijing Normal Univ, Dept Astron, Beijing 100088, Peoples R China
[5] Tsinghua Univ, Dept Astron, Beijing 100084, Peoples R China
[6] Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China
[7] Tsinghua Univ, Dept Engn Phys, Beijing 100084, Peoples R China
[8] Chinese Acad Sci, Natl Astron Observ, Key Lab Space Astron & Technol, Beijing 100012, Peoples R China