[1] Chinese Acad Sci, Natl Astron Observ, 20A Datun Rd, Beijing 100101, Peoples R China
[2] CSIRO Astron & Space Sci, POB 76, Epping, NSW 1710, Australia
[3] Univ Chinese Acad Sci, Beijing 100049, Peoples R China
[4] Xinjiang Astron Observ, 150,Sci 1 St, Urumqi 830011, Xinjiang, Peoples R China
[5] Chinese Acad Sci, Key Lab Radio Astron, 150 Sci 1 St, Urumqi 830011, Xinjiang, Peoples R China
[6] Xinjiang Key Lab Radio Astrophys, 150 Sci 1 St, Urumqi 830011, Xinjiang, Peoples R China
[7] Victoria Univ Wellington, POB 600, Wellington 6140, New Zealand
[8] Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany
[9] Natl Res Council Canada, Dominion Radio Astrophys Observ, Herzberg Res Ctr Astron & Astrophys, POB 248, Penticton, BC V2A 6J9, Canada
[10] Guizhou Normal Univ, Guizhou Prov Key Lab Radio Astron & Data Proc, Guiyang 550001, Peoples R China
[11] Guizhou Normal Univ, Sch Phys & Elect Sci, Guiyang 550001, Peoples R China
[12] Peking Univ, Kavli Inst Astron & Astrophys, Beijing 100871, Peoples R China
[13] Peking Univ, Sch Phys, Dept Astron, Beijing 100871, Peoples R China
[14] Chinese Acad Sci, Purple Mt Observ, Nanjing 210008, Peoples R China
[15] Univ Western Australia, Int Ctr Radio Astron Res, Crawley, WA 6009, Australia
[16] Univ Manchester, Ctr Astrophys, Jodrell Bank, Alan Turing Bldg,Oxford Rd, Manchester M13 9PL, Lancs, England
[17] Nanjing Univ, Sch Astron & Space Sci, 163 Xianlin Ave, Nanjing 210023, Peoples R China