VLBI observations, summarised in Table 4.1, were made using the SHEVE (plus Shanghai) array of telescopes. All data were obtained and processed as described in chapter 2.
Table 4.1: Observation log for EGRET and non-EGRET sources
Brightness temperatures in the observer's frame were estimated from the images, for radio core components de-convolved from the synthesised beam using the JMFIT task in AIPS. JMFIT fits elliptical Gaussians to components and returns only an upper limit on the Gaussian FWHM of unresolved components but returns an estimated FWHM, with upper and lower limits, for components which are resolved. JMFIT also returns the integrated flux density of the component. In the case of unresolved core components, lower limits to the observed brightness temperature were derived using the flux density and the upper limit to the FWHM. For the cores which were resolved, an estimate of the observed brightness temperature could be derived from the estimated FWHM and the flux density. Using the source red shifts, brightness temperatures were then derived in the source frame.
For PKS 0521-365 high-resolution multi epoch and multi frequency data are available, and so, in addition to the above procedures, the following analyses were performed. Limits on the jet to counterjet surface brightness ratios were made directly from the images. Spectral indices, using total flux densities measured from the images, were estimated. The multi epoch data were used to estimate the apparent speed in the jet of PKS 0521-365. To this end the Caltech task MODELFIT was used to fit simple Gaussian components to the visibility amplitudes and closure phases, either two or three components at each epoch, keeping the core component as the arbitrary phase centre.
