1. INAF - Istituto di Radioastronomia, Bologna Via Gobetti 101, I-40129 Bologna, Italy
2. Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029, Hamburg, Germany
3. Dipartimento di Fisica e Astronomia, Universitá di Bologna, via P. Gobetti 93/2, I-40129, Bologna, Italy
4. Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 452 Lomita Mall, Stanford, California 94305-4085, USA
5. Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305-4060, USA
6. CSIRO Astronomy & Space Science, 26 Dick Perry Avenue, Kensington, WA, 6151, Australia
7. Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, The Netherlands
8. Oxford e-Research Centre (OeRC), Department of Engineering Science, University of Oxford, Oxford, OX1 3QG, UK
9. Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands
10. Observatoire de la Côte d’Azur, Laboratoire Lagrange UMR 7293. Bd. de l’Observatoire, CS 34229 F-06304 Nice, France
11. ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands