[1] Univ Toulouse, IRAP, CNRS, CNES,UPS, Toulouse, France
[2] CNES, 18 Ave Edouard Belin, F-31400 Toulouse, France
[3] Osserv Astron Trieste, INAF, Via Tiepolo 11, I-34131 Trieste, Italy
[4] Univ Trieste, Dipartimento Fis, Sez Astron, Via Tiepolo 11, I-34131 Trieste, Italy
[5] INFN Natl Inst Nucl Phys, Via Valerio 2, I-34127 Trieste, Italy
[6] Univ Observ Munich, Scheinerstr 1, D-81679 Munich, Germany
[7] Max Planck Inst Astrophys, Karl Schwarzschield Str 1, D-85748 Garching, Germany
[8] Univ Bologna, Dipartimento Fis & Astron, Via Gobetti 93, I-40127 Bologna, Italy
[9] Osservatorio Astrofis & Sci Spazio, INAF, Via Pietro Gobetti 93-3, I-40129 Bologna, Italy
[10] Ist Nazl Fis Nucl, Sez Bologna, Viale Berti Pichat 6-2, I-40127 Bologna, Italy
[11] Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA
[12] Harvard Smithsonian Ctr Astrophys, 60 Garden St, Cambridge, MA 02138 USA
[13] Dr Karl Remeis Observ, Sternwartstr 7, D-96049 Bamberg, Germany
[14] Erlangen Ctr Astroparticle Phys, Sternwartstr 7, D-96049 Bamberg, Germany