Institution: | MSSL, University College London, Holmbury St Mary, Surrey RH5 6NT;Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA;Observatoire de Strasbourg, 11, rue de l'Université, Strasbourg F-67000, France;Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA |