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Costa, Marco Ernesto 1989 , 'Southern pulsars', PhD thesis, University of Tasmania.

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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°±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 —2uGauss 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 —20° 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.

Item Type: Thesis - PhD
Authors/Creators:Costa, Marco Ernesto
Keywords: Pulsars
Copyright Holders: The Author
Copyright Information:

Copyright 1989 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1990. Bibliography: p. 246-253

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