1. INAF – Osservatorio Astronomico di Cagliari , Via della Scienza 5, I-09047 Selargius , Italy
2. INAF – Istituto di Radioastronomia , Via P. Gobetti 101, I-40129 Bologna , Italy
3. Dipartimento di Fisica e Astronomia, Università di Bologna , Via P. Gobetti 93/2, I-40129 Bologna , Italy
4. Agenzia Spaziale Italiana (ASI) , Via del Politecnico snc, I-00133 Roma
5. Department of Physics and Electronics, Rhodes University , PO Box 94, Grahamstown 6140 , South Africa
6. South African Radio Astronomy Observatory , Black River Park, 2 Fir Street, Observatory, Cape Town 7925 , South Africa
7. Fundación G. Galilei – INAF TNG , Rambla J. A. Fernández Pérez 7, E-38712 Breña Baja (La Palma) , Spain
8. Instituto de Astrofísica de Canarias , C/Vía Láctea s/n, E-38205 La Laguna (Tenerife) , Spain
9. Dep. de Astrofísica, Univ. de La Laguna , Av. del Astrofísico Francisco Sánchez s/n, E-38205 La Laguna (Tenerife) , Spain
10. INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna , Via P. Gobetti 93/3, I-40129 Bologna , Italy
11. U.S. Naval Research Laboratory , Washington, DC 20375 , USA
12. Max Planck Institut für Astrophysik , Karl-Schwarzschild-Str.1, D-85740 Garching , Germany
13. Laboratoire Lagrange, UCA, OCA, CNRS , Blvd de l’Observatoire, CS 34229, F-06304 Nice cedex 4 , France
14. INAF – IASF Milano , Via Bassini 15, I-20133 Milano , Italy
15. Dip. di Fisica, Università degli Studi di Trieste – Sezione di Astronomia , Via Tiepolo 11, I-34143 Trieste , Italy
16. INAF – Osservatorio Astronomico di Trieste , Via Tiepolo 11, I-34143 Trieste , Italy
17. International Centre for Radio Astronomy Research (ICRAR) , Curtin University, Bentley, WA 6102 , Australia
18. ASTRON, the Netherlands Institute for Radio Astronomy , Postbus 2, NL-7990 AA, Dwingeloo , the Netherlands
19. National Radio Astronomy Observatory , P.O. Box O, Socorro, NM 87801 , USA
20. Department of Physics and Astronomy, University of New Mexico , Albuquerque NM 87131 , USA