P. A. Hamilton

Pulsar Timing Observations at Tidbinbilla

Pulse arrival time measurements allow the determination of accurate pulsar periods, period derivatives and, provided the data span is at least one year, precise pulsar positions. If observations are frequent and reasonably regular, irregularities in the period can also be investigated. To minimize the effect of possible variations in dispersion measure, it is important that these observations be made at a relatively high frequency, preferably above 1 GHz. To eliminate pulse shape variations due to variable ionospheric Faraday rotation, the pulse total intensity or one of the circular polarizations must be recorded.

Interstellar Scattering and the Pulse from the Vela Pulsar

Measurements of PSR 0833-45 were made at wavelengths of 21, 48, 73 and 100 cm. Pulse broadening proportional to about the fourth power of the wavelength was found, consistent with multipath scattering in the interstellar medium. It is further concluded that the rotation measure was constant at 33.2 rad m−2 across this wavelength range, supporting the conclusion that the radiation originates in the vicinity of a magnetic pole.