Institution: | aAstrophysikalisches Institut Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany bHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA cX-ray Astronomy Group, University of Leicester, University Road, Leicester LE1 7RH, UK dMax-Planck Institut für extraterrestrische Physik, 85748 Garching, Germany |