1. Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
2. School of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
3. South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
4. Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
5. Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
6. Inter-University Institute for Data Intensive Astronomy, Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa