Pulsar timing observations at Tidbinbilla.

The observing system used for regular timing observations of 19 pulsars at the NASA Deep Space Station, Tidbinbilla, Australia, is described, and the results obtained so far are discussed. The observations are made with a 26-m diameter antenna at a frequency of 2295 MHz; right-circular polarization is recorded, and an on-line computer samples the detector output and accumulates an integrated profile for 1 to 5 min before writing the data on magnetic tape. Parameters obtained from the timing observations for five of the more frequently observed pulsars are listed, including the period derivatives. Observations of arrival times for the Vela pulsar are reported which show a discontinuous decrease in period. Arrival-time residuals for the prejump and postjump data are plotted, and a characteristic decay time of 165 years is determined for the period derivative. It is suggested that the period of the Vela pulsar will not return to its equilibrium rate of increase for several years and will remain offset from the extrapolated prejump value by about 80% of the initial period decrease.