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Abstract

This thesis describes a new technique for observing pulsar micro-structure,
which is a class of random fluctuations in pulsar radio-emission
on timescales less than one millisecond. Using this technique observations
were made with a time resolution of 0.5 μs. No new phenomena were revealed
by the improvement in time resolution over that used by other workers.
However the first measurement of the microstructure timescale of pulsar
PSR 1749-28 was obtained.
The design of the equipment and the computer processing involved in
the method are described in the thesis. In this method -pulsar signals in a
bandwidth of 2 MHz are mixed to baseband and recorded on videotape. Subsequently
selected parts of the tape are digitized using the stop action
facility of the recorder and an interleaved sampling scheme. The effects
of interstellar dispersion are removed by computer processing yielding the
maximal time resolution 1/B where B is the bandwidth, that is, 2 MHz. This
method avoids the normal restriction, imposed by the speed of the digitizer,
that applies when digitizing is done in real time, namely that the bandwidth
must be restricted to half the sample rate.
Recordings were made of signals received by the Molonglo radiotelescope
at 408 MHz from 15 pulsars. A total of 22 pulses from four different
pulsars were strong enough and otherwise suitable for analysis. Each
pulse involves 86000 samples, that is, a time window of 20 ms sampled at an
effective rate of 4.5 MHz.
The pulses were analyzed at time resolutions down to 0.5 μs and the
dynamic spectrum of each in an observing window 15 ms x 2 MHz was obtained.
A search was made for frequency-time structures such as those produced by
moving,radiating sources and by interference effects in the pulsar magnetosphere.
Such structures were not observed.
Auto-correlation and cross-correlation analyses were carried out on
the data. The results for PSR 0950+08 agree with those obtained by other
workers. A characteristic microstructure timescale of 250 ± 50 μs was
obtained from the auto-correlation of the power spectrum of PSR 1749-28.
All of the observations are consistent with the amplitude-modulated
noise (AMN) model of Rickett (1975) together with interstellar scintillation.
One particular pulse from PSR 0950+08 was analyzed in great detail
because some large unresolved intensity fluctuations were apparent. Single
intense impulses are not consistent with the ANN model and would be of some
astrophysical interest if found. A series of tests were applied to the data;
it is concluded that such impulses were not observed.
The relationship of the ANN model to pulsar emission theories and the
direction of future research are discussed.

Item Type:	Thesis - PhD
Authors/Creators:	Allen, RK
Keywords:	Pulsars
Copyright Holders:	The Author
Copyright Information:	Copyright 1979 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, 1980. Includes references
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