1. Shanghai Astronomical Observatory, CAS , 80 Nandan Road, Shanghai 200030, China
2. School of Astronomy and Space Sciences, University of Chinese Academy of Sciences , No. 19A Yuquan Road, Beijing 100049, China
3. Kavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, China
4. Department of Astronomy, School of Physics, Peking University , Beijing 100871, China
5. Xinjiang Astronomical Observatory, Chinese Academy of Sciences , 150 Science 1-Street, 830011 Urumqi, China
6. Netherlands Institute for Radio Astronomy ASTRON , NL-7991 PD Dwingeloo, the Netherlands
7. SKA Observatory, Jodrell Bank, Lower Withington , Macclesfield SK11 9FT, UK
8. Physics Department, Technion - Israel Institute of Technology , Haifa 3200003, Israel
9. Korea Astronomy and Space Science Institute , 776 Daedeok-daero, Yuseong-gu, Daejeon 34055, Korea
10. Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory , SE-439 92 Onsala, Sweden