1. Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
2. Bendenweg 51, D-53121 Bonn, Germany
3. Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
4. INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy
5. INAF – Istituto di Radioastronomia, Via Gobetti 101, I-40129 Bologna, Italy
6. Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada
7. Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands