[1] INTEGRAL Sci Data Ctr, CH-1290 Versoix, Switzerland
[2] Observ Geneva, CH-1290 Sauverny, Switzerland
[3] Univ Southampton, Sch Phys & Astron, Southampton SO17 1BJ, Hants, England
[4] CNR, IASF, I-40129 Bologna, Italy
[5] CEA Saclay, DAPNIA, Serv Astrophys, F-91191 Gif Sur Yvette, France
[6] Coll France, Federat Rech APC, F-75231 Paris, France
[7] CNR, IASF, I-00133 Rome, Italy