[1] IASF, INAF, via Ugo la Malfa 153, 90136 Palermo, Italy
[2] IAAT, Abt. Astronomie, Universität Tübingen, Sand 1, 72076 Tübingen, Germany
[3] Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
[4] INTEGRAL Science Data Centre, 16 Ch. d'Écogia, 1290 Versoix, Switzerland
[5] Space Research Center, Bartycka 18a, 00716 Warsaw, Poland
[6] Dr. Remeis Sternwarte, Astronomisches Institut, University of Erlangen-Nuremberg, Sternwartstr. 7, 96049 Bamberg, Germany