Timing observations of the Vela pulsar, PSR0833-45

The analysis is presented of pulse arrival time measurements of the Vela pulsar, PSR0833-45, obtained principally from near-daily observations conducted at the Llanherne Radiophysics Observatory (LRO) between October, 1981, and September, 1986. During this interval, the secular decrease in the rotation rate of the pulsar was interrupted by glitch events which occurred in October, 1981, August, 1982, and July, 1985. Each glitch was accompanied by an abrupt change in rotation frequency of fractional magnitude Aviv -2x10‚ÄövÖ¬™‚ÄövÖ‚àÇ of which less than 10% decayed within a subsequent interval of one year. The characteristics of these events were similar to those reported for the four previous glitches of the Vela pulsar. However, because of the regularity of the LRO observations, sufficient post-jump data were obtained to allow the reappraisal of the existing glitch models. The timing obtained immediately prior to each glitch were found to be completely devoid of any distinctive precursor signatures above the level of measurement noise, even to within one hour of the July, 1985, glitch. In addition, there were no significant changes in the characteristics of the radio emission about the time of each glitch. The timing signature of each glitch was investigated in terms of the existing viable models. The two-component model was rejected on the grounds of its inability to account for the long term relaxation behaviour. In addition, there was no evidence of the decoupling time predicted by the vortex creep model. The phase noise on timescales less than 6 hours was found to exhibit excess power in comparison with the expectation from measurement uncertainties. There was no evidence for any significant systematic behaviour of the autocorrelation function of the phase fluctuations with respect to time lag. Evidence was found that the excess noise has a power-law dependence on observing frequency, which may be a result of magnetospheric processes. Dual frequency measurements made between March and September, 1986, have for the first time enabled the character of short timescale variations in the dispersion delay along the path to the pulsar to be determined. The measurements are consistent with the motion of the line-of-sight through a region of inhomogeneous plasma located within the Gum Nebula.