1. Anton Pannekoek Institute for Astronomy, University of Amsterdam , Science Park 904, NL-1098 XH Amsterdam , the Netherlands
2. ASTRON, Netherlands Institute for Radio Astronomy , Oude Hoogeveensedijk 4, NL-7991 PD Dwingeloo , the Netherlands
3. Joint Institute for VLBI ERIC , Oude Hoogeveensedijk 4, NL-7991 PD Dwingeloo , the Netherlands
4. CSIRO Space and Astronomy, Australia Telescope National Facility , PO Box 76, Epping, NSW 1710 , Australia
5. MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology , 77 Massachusetts Ave, Cambridge, MA 02139 , USA
6. Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory , SE-439 92 Onsala , Sweden
7. Max-Planck-Institut für Radioastronomie , Auf dem Hügel 69, D-53121 Bonn , Germany
8. Engineering Research Institute Ventspils International Radio Astronomy Centre of Ventspils University of Applied Sciences , Inženieru street 101, Ventspils LV-3601 , Latvia
9. McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University , Pittsburgh, PA 15213 , USA
10. Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester , Manchester M13 9PL , UK
11. INAF – Istituto di Radioastronomia , Via Gobetti 101, I-40129 Bologna , Italy
12. INAF – Osservatorio Astronomico di Cagliari , via della Scienza 5, I-09047 Selargius (CA) , Italy
13. Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University , Grudziadzka 5, PL-87-100 Toruń , Poland
14. Xinjiang Astronomical Observatory , CAS, 150 Science 1-Street, Urumqi, Xinjiang 830011 , China