[1] CEA, DSM, DAPNIA, Serv Astrophys, F-91191 Gif Sur Yvette, France
[2] Inst Astron & Fis Espacio, RA-1428 Buenos Aires, DF, Argentina
[3] Univ Hawaii, Inst Astron, Honolulu, HI 96822 USA
[4] Max Planck Inst Extraterr Phys, D-85740 Garching, Germany
[5] Univ Nacl La Plata, Fac Ciencias Astron & Geofis, RA-1900 La Plata, Argentina
[6] Int Gamma Ray Astrophys Lab, Sci Data Ctr, CH-1290 Versoix, Switzerland
[7] Observ Geneva, CH-1290 Sauverny, Switzerland
[8] Ist Astrofis Spaziale & Fis Cosm, I-20133 Milan, Italy
[9] European So Observ, Santiago 19, Chile