[1] CALTECH, 1200 E Calif Blvd, Pasadena, CA 91125 USA
[2] Joint Inst VLBI ERIC, POB 2, NL-7990 AA Dwingeloo, Netherlands
[3] Lomonosov Moscow State Univ, Sternberg Astron Inst, Univ Av 13, Moscow 119991, Russia
[4] Netherlands Inst Radio Astron, ASTRON, Postbus 2, NL-7990 AA Dwingeloo, Netherlands
[5] Aalto Univ, Sch Elect Engn, Dept Radio Sci & Engn, Espoo 02150, Finland
[6] Delft Univ Technol, Dept Astrodynam & Space Missions, NL-2629 HS Delft, Netherlands
[7] Shanghai Astron Observ, 80 Nandan Rd, Shanghai 200030, Peoples R China
[8] Carnegie Mellon Univ, 5000 Forbes Ave, Pittsburgh, PA 15213 USA
[9] Inst Space Sci, Atomistilor 409,POB MG-23, Bucharest 077125, Romania
[10] Royal Observ Belgium, Ringlaan 3, B-1180 Brussels, Belgium
[11] CNES GRGS, OMP 14 Ave Edouard Belin, F-31400 Toulouse, France
[12] UPMC Lille 1, CNRS, PSL Res Univ, UMR CNRS 8028,IMCCE,Observ Paris, 77 Av Denfert Rochereau, F-75014 Paris, France
[13] Observ Yebes IGN, Apartado 148, Guadalajara 19180, Spain
[14] Hartebeesthoek Radio Astron Observ, ZA-1740 Krugersdorp, South Africa
[15] Geodet Observ Wettzell, Fed Agcy Cartog & Geodesy, D-60598 Frankfurt, Germany
[16] Chalmers Univ Technol, Dept Earth & Space Sci, Onsala Space Observ, S-43992 Onsala, Sweden
[17] Radio Observ Medicina, Natl Inst Astrophys, Radio Astron Inst, I-75500 Medicina, Italy
[18] Russian Acad Sci, Inst Appl Astron, Kutuzova Embankment 10, St Petersburg 191187, Russia
[19] Univ Tasmania, Sch Phys Sci, Private Bag 37, Hobart, Tas 7001, Australia
[20] Australia Telescope Natl Facil, CSIRO Astron & Space Sci, Narrabri, NSW 2390, Australia
[21] Auckland Univ Technol, Inst Radio Astron & Space Res, Private Bag 92006, Auckland 1142, New Zealand
[22] Chinese Acad Sci, Xinjiang Astron Observ, Urumqi 830011, Peoples R China
[23] Chinese Acad Sci, Yunnan Astron Observ, Kunming 650011, Peoples R China
[24] Aalto Univ, Metsahovi Radio Observ, Kylmala 02540, Finland
[25] European Space Agcy ESA ESTEC Sci Support Off, NL-2200 AG Noordwijk, Netherlands