1. Yunnan Observatories, Chinese Academy of Sciences, 650216 Kunming, Yunnan, China
2. University of Chinese Academy of Sciences, 19A Yuquan Road, Shijingshan District, 100049 Beijing, China
3. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650216 Kunming, China
4. Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden
5. Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, China
6. Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 210009 Nanjing, China
7. Joint Institute for VLBI ERIC (JIVE), Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
8. Centre for Astrophysics, and Supercomputing, Swinburne University of Technology, John St, Hawthorn, VIC 3122, Australia
9. CSIRO Astronomy and Space Science, Kensington, WA 6151, Australia