1. Department of Physics, Faculty of Science, Khon Kaen University, 123 Moo 16, T. Nai-Muang, A. Muang, Khon Kaen 40002, Thailand
2. International Centre for Radio Astronomy Research, The University of Western Australia, M468, 35 Stirling Highway, Crawley, Perth, WA 6009, Australia
3. National Astronomical Research Institute of Thailand, 260 Moo 4, T. Donkaew, A. Maerim, Chiangmai 50180, Thailand
4. CSIRO Astronomy and Space Science, 26 Dick Perry Avenue, Kensington WA 6151, Australia
5. Observatorio Astronómico Nacional (IGN), Alfonso XII, 3 y 5, E-28014 Madrid, Spain
6. CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
7. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany