1. Universitá degli Studi di Cagliari, Dipartimento di Fisica, SP Monserrato-Sestu km 0.7, I-09042 Monserrato (CA), Italy
2. INAF-Osservatorio Astronomico di Cagliari, via della Scienza 5, I-09047, Selargius (CA), Italy
3. INAF-Istituto di Radio Astronomia, via Gobetti 101, I-40129 Bologna, Italy
4. South African Radio Astronomy Observatory, Black River Park, 2 Fir Street, Observatory, Cape Town, 7925, South Africa
5. Department of Physics and Electronics, Rhodes University, PO Box 94, Makhanda, 6140, South Africa
6. INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti, 93/3, I-40129, Bologna, Italy
7. Institute of Space Sciences and Astronomy (ISSA), University of Malta, Msida MSD 2080, Malta
8. Dipartimento di Fisica e Astronomia, Universitá di Bologna, Via Gobetti 93/2, I-40129 Bologna, Italy
9. INAF/IAPS, via del Fosso del Cavaliere 100, I-00133 Roma (RM), Italy
10. INFN Sezione di Roma 2, via della Ricerca Scientifica 1, I-00133 Roma (RM), Italy
11. Department of Astronomy, University of California Berkeley, Berkeley, CA 94720, USA
12. Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, D-85748 Garching bei München, Germany
13. MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA
14. Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA 02139, USA
15. Universitá degli Studi di Roma ‘Tor Vergata’, via della Ricerca Scientifica 1, I-00133 Roma (RM), Italy
16. SSDC/ASI, via del Politecnico snc, I-00133 Roma (RM), Italy
17. INAF-Osservatorio Astronomico di Roma, via Frascati 33, I-00078 Monte Porzio Catone (RM), Italy