1. Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University , Shanghai 200240 , People’s Republic of China
2. Key Laboratory for Particle Astrophysics and Cosmology (MOE) , Shanghai 200240 , China
3. Shanghai Key Laboratory for Particle Physics and Cosmology , Shanghai 200240 , China
4. Shanghai Astronomical Observatory (SHAO) , Nandan Road 80, Shanghai 200030 , China
5. University of Chinese Academy of Sciences , Beijing 100049 , China