GT thanks Allen Shafter for discussing details of the reduction technique and providing parts of the analysis code. The authors are grateful to R. Schwarz and to the referee M. Mouchet for valuable comments and discussions which considerably improved the presentation of our results. This work was partially financed by the DGAPA project IN109195. JG is supported by the Deutsche Agentur für Raumfahrtangelegenheiten (DARA) GmbH under contract FKZ 50 OR 9201 and 50 QQ 9602 3. The ROSAT project is supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DARA) and the Max-Planck-Society.
© European Southern Observatory (ESO) 1997
Online publication: March 26, 1998