High-precision observations of relativistic binary and millisecond pulsars

The technique of pulsar timing reveals a wealth of new information when a precision of ~1 μs or better is reached, but such precision is difficult to achieve. This thesis describes a series of very high precision timing observations that improve our knowledge of the targeted pulsar systems. We begin by describing a newly-developed baseband recording and coherent dedispersion system (CPSR2), along with a new object-oriented software development environment for pulsar data processing. Data obtained with this new instrument during a 3 year observing campaign at the Parkes 64m radio telescope are analysed in a number of novel ways. The mean profile of PSR J1022+1001 is shown to be stable on timescales of a few minutes, in contrast with previously published claims. We obtain a level of precision an order of magnitude better than any previous timing of this pulsar. In addition, we observe dramatic changes in the mean profile of the relativistic binary pulsar J1141–6545, which broadens by ~50% over the time span of our observations. This is interpreted as evidence for secular evolution of the line of sight to the emission cone, caused by General relativistic geodetic precession which tilts the spin axis of the pulsar. High precision CPSR2 observations of the extraordinary double pulsar binary system are presented and we construct calibrated, mean polarimetric profiles for PSR J0737–3039A, in two frequency bands. These profiles provide a reference against which future profile evolution may be detected, given that we expect geodetic precession to alter the observed mean profile on an even shorter time scale than for PSR J1141–6545. The bulk of this thesis involves timing a selection of millisecond pulsars whose physical characteristics should allow the highest precision to be obtained. We measure several new proper motions and parallax distances. Shapiro delay is used to constrain the inclination angles and component masses of several of the binary systems in our source list. In addition, subtle periodic variations of the orbital parameters of two nearby binary millisecond pulsars are detected and attributed to annual orbital parallax, providing additional constraints on their three-dimensional orbital geometries. Future observations of these two sources may lead to more stringent tests of post-Keplerian gravitational theories. Finally, we use the timing residuals of one very stable source (PSR J1909–3744) as a reference against which we time PSR J1713+0747 with a root-mean-square precision of 133 ns, amongst the best timing residuals ever obtained. This result is an important step in the search for long-period gravitational waves using pulsar timing arrays.