We are grateful to the Director of HartRAO G.D. Nicolson for making the HartRAO pulsar data available to us, and to C.S. Flanagan who set up the HartRAO pulsar programme and acquired most of the data. TVSH thanks Yu.P. Shitov for valuable comments and the staff of PRAO for assistance in the observations. This work was supported by grant INTAS 96-0154. JOU acknowledges the hospitality and support of HartRAO. IAU Commission 38 grant enabled him to visit South Africa. We thank the referee for helpful comments and suggestions.
© European Southern Observatory (ESO) 2000
Online publication: February 25, 2000