1. Max Planck Institut f ur Radioastronomie, Auf dem Hugel 69, Bonn D-53121, Germany
2. INAF, Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy
3. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn VIC 3122, Australia
4. ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), Mail H29, Swinburne University of Technology, PO Box 218, Hawthorn VIC 3122, Australia
5. South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory 7925, South Africa
6. Universitá di Cagliari, Dipartimento di Fisica, S.P. Monserrato-Sestu Km 0,700, I-09042 Monserrato (CA), Italy
7. Department of Physics and Astronomy, University of the Western Cape, Bellville, Cape Town 7535, South Africa
8. Jodrell Bank Centre for Astrophysics, Department of Physics & Astronomy, The University of Manchester, Manchester M13 9PL, UK