Affiliation: | 1X-Ray Astronomy Group, Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH;2Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, the Netherlands;3Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy |