1. Max-Planck-Institut für extraterrestrische Physik , Giessenbachstrasse 1, 85748 Garching , Germany
2. School of Physics and Astronomy & Institute for Gravitational Wave Astronomy, University of Birmingham , Birmingham B15 2TT , UK
3. International Centre for Radio Astronomy Research, Curtin University , GPO Box U1987, Perth, WA 6845 , Australia
4. South African Astronomical Observatory , PO Box 9, Observatory Rd, 7935 Observatory, Cape Town , South Africa
5. Department of Astronomy, University of Cape Town , Private Bag X3, Rondebosch 7701 , South Africa
6. Department of Physics, University of the Free State , PO Box 339, Bloemfontein 9300 , South Africa