[1] Univ London Imperial Coll Sci Technol & Med, Blackett Lab, Astrophys Grp, London SW7 2AZ, England
[2] Charles Sturt Univ, Sch Comp & Math, Wagga Wagga, NSW 2678, Australia
[3] IASF Bologna, INAF, I-40129 Bologna, Italy
[4] ESA, ESAC, XMM, Newton Sci Operat Ctr, E-28080 Madrid, Spain
[5] Max Planck Inst Astrophys, D-85741 Garching, Germany