1. Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Beijing, China;
2. Department of Physics, University of Chinese Academy of Sciences, Beijing, China
3. Tianfu Cosmic Ray Research Center, Chengdu, China
4. School of Astronomy and Space Science, Nanjing University, Nanjing, China
5. Key Laboratory of Modern Astronomy and Astrophysics, Ministry of Education, Nanjing University, Nanjing, China
6. Department of Astronomy, University of Science and Technology of China, Hefei, China