1. Department of Physics and Astronomy ‘G. Galilei’, University of Padova, Via Marzolo, 8, I-35131 Padova, Italy
2. INAF – Astronomical Observatory of Padova, Vicolo dell’ Osservatorio 5, I-35122 Padova, Italy
3. Department of Physics, University of Atacama, Copayapu 485, Copiapo, Chile
4. Leiden Observatory, Leiden University, Neils Bohrweg 2, NL-2333 CA Leiden, the Netherlands
5. ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7900 AA Dwingeloo, the Netherlands
6. TIFPA – Trento Institute for Fundamentals Physics Applications, Via Sommarive 14, I-38123 Povo, Italy