The authors would especially like to thank Joachim Wambsganss for making available and giving support in using his microlensing code. They thank Frank Briggs for providing useful supermongo code, and Joachim Wambsganss, Jane Dennett-Thorpe, Penny Sackett, Jean-Pierre Macquart and Roger Blandford for useful discussions. They also thank the referee, Andreas Quirrenbach, for pointing out several important issues. LVEK and AGdeB acknowledge the support from an NWO program subsidy (grant number 781-76-101). This research was supported in part by the European Commission, TMR Programme, Research Network Contract ERBFMRXCT96-0034 `CERES'. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Westerbork Synthesis Radio Telescope (WSRT) is operated by the Netherlands Foundation for Research in Astronomy (ASTRON) with the financial support from the Netherlands Organization for Scientific Research (NWO).
© European Southern Observatory (ESO) 2000
Online publication: June 20, 2000