1. Kapteyn Astronomical Institute, University of Groningen , Landleven 12, NL-9747 AV Groningen, the Netherlands
2. Department of Physics and Astronomy, University of the Western Cape , Robert Sobukwe Road, Bellville 7535, South Africa
3. INAF – Osservatorio Astronomico di Padova , Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
4. INAF – Osservatorio Astronomico di Cagliari , Via della Scienza 5, I-09047 Selargius (CA), Italy
5. Department of Physics and Electronics, Rhodes University , PO Box 94, Makhanda 6140, South Africa
6. ASTRON, the Netherlands Institute for Radio Astronomy , Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
7. Faculty of Physics and Astronomy, Astronomical Institute, Ruhr University Bochum , Universitätsstr 50, D-44801 Bochum, Germany
8. Department of Astronomy, University of Cape Town , Private Bag X3, Rondebosch 7701, South Africa
9. Department of Physics and Astronomy, West Virginia University , PO Box 6315, Morgantown, WV 26506, USA
10. Center for Gravitational Waves and Cosmology, West Virginia University , Chestnut Ridge Research Building, Morgantown, WV 26505, USA
11. Instituto de Física y Astronomía, Universidad de Valparaíso , Avda. Gran Bretãna 1111 Valparaíso, Chile
12. Dipartimento di Fisica e Astronomia, Università di Bologna , via Gobetti 93/2, I-40129 Bologna, Italy
13. INAF, Istituto di Radioastronomia di Bologna , via Gobetti 101, I-40129 Bologna, Italy