Southern pulsars

A digital parallel processor has been constructed for use with a wide-band polarimeter. The processor contains five high-speed digital signal microprocessors with a combined execution speed of 25million instructions-per-second. Four of the microprocessors are configured in parallel as a high-speed processing stage for the data emerging from the polarimeter and the fifth controls an interface to an observatory computer. With this observing system data has been collected in the form of superposed epoch integrations and single pulses from the pulsars. To collect the single pulses the parallel processor calibrated, derotated and dedispersed the pulsar data in real-time. Superposed epoch integrations were collected from 27 pulsars at observing frequencies in the range 600 to 666MHz. For 16 of these pulsars no polarisation data has previously been published so the pool of pulsar polarisation data has been expanded. The polarisation data was analysed to yield the rotation measures of the pulsars and brings to a total of 200 the number of pulsars for which rotation measures are now known. A pulsar of particular interest has been identified; mode changing has been observed in PSR1056-57. Over the course of two integrations the profile of this pulsar changed shape by adding a pair of weak outrider pulses and a linearly and circularly polarized feature in the centre of the main profile. The pulsar rotation measures have been used to investigate the structure of the Galactic magnetic field. That study found the peak magnetic field strength is 4.3¬¨¬±0.2u.Gauss directed towards Galactic longitude l = 73¬¨‚àû¬¨¬±6'' and offers the first direct evidence that the large scale field is confined to the spiral features of the Galaxy. As a result of this investigation there is reason to question the distance scale to pulsars behind the North Polar Spur magnetic bubble; the suggestion is that the electron distribution model of the Galaxy should be modified to account for the North Polar Spur and as a result the distances to pulsars in this direction might be reduced by as much as a factor of ten. One of the pulsars in this study is in the Large Magellanic Cloud. Its rotation measure has been evaluated as 4¬¨¬±5rad m-2 which, together with its dispersion measure and correction for the Galactic foreground, leads to an estimate of ‚ÄövÑvÆ2uGauss for the sightline magnetic field strength in LMC. This is the first measurement of the strength of the large scale field in that galaxy. Scintillations have been detected for the first time in pulsar PSR0538-75. The decorrelation bandwidth and decorrelation time of those scintillations has led to an estimate of the pulsar's transverse velocity as 120km s-1. Further changes have been measured in the rotation measure of pulsar PSR0833-45. The changes are attributed to a magnetised filament in the Vela supernova remnant moving past the line-of-sight. The observed changes are consistent with a change in the magnetic field's orientation which brings it ‚ÄövÑvÆ20¬¨‚àû closer to the sightline. Single pulses have been collected from the Vela pulsar, PSR0833-45. These show that the stronger pulses have smaller halfwidths and arrive earlier than the weaker pulses. Also, the position angles of the linearly polarized feature in the stronger pulses appear to swing through a smaller angle. As a result of these observations an emission region model is suggested in which the stronger pulses are emitted further from the magnetic axis and at earlier pulsar longitudes.