1. Department of Physics, University of York , York YO10 5DD, UK
2. School of Physics, University of the Witwatersrand , Johannesburg 2050, South Africa
3. iThemba LABS, National Research Foundation , PO Box 722, Somerset West 7129, South Africa
4. Cyclotron Institute, Texas A&M University , College Station, Texas, TX 77843, USA
5. Department of Physics and Astronomy, Texas A&M University , College Station, Texas, TX 77843, USA
6. Department of Physics North Carolina State University , Raleigh, North Carolina, NC 27695-8202, USA
7. Triangle Universities Nuclear Laboratory , Durham, North Carolina, NC 27708-0308, USA
8. TRIUMF , 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada
9. Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles , CP 226, B-1050 Brussels, Belgium
10. Astrophysics Group , Lennard-Jones Laboratories, Keele University, Keele ST5 5BG, UK
11. Kavli IPMU (WPI), The University of Tokyo , Kashiwa, Chiba 277-8583, Japan