1. School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
2. School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
3. Dipartimento di Fisica, Università degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, I-09042 Monserrato, Italy
4. Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy
5. Department of Physics, Royal Holloway, University of London, Egham TW20 0EX, UK
6. Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH, Amsterdam, the Netherlands
7. Department of Physics, Nagoya University, Aichi 464-8602, Japan
8. HAL24K, Building B.3, Johan Huizingalaan 400, NL-1066 JS Amsterdam, the Netherlands