Institution: | (1) Center for Space Research and Department of Physics, Massachusetts Institute of Technology, Room 37-627, 02139 Cambridge, MA, USA;(2) Astronomical Institute Anton Pannekoek , University of Amsterdam, oetersstraat 15, 1018 WB Amsterdam, The Netherlands;(3) EXOSAT Observatory, Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands |