We would like to thank Andrzej Marecki for very careful and critical reading of the manuscript.
We thank Maria Rioja for the data correlation.
We thank also Fredrik T Rantakyrö and Hardip Sanghera for important suggestions and help in calibrating of amplitudes of the EVN data.
We are particularly grateful Dr Strom for valuable comments on the manuscript.
© European Southern Observatory (ESO) 1998
Online publication: May 15, 1998