PKS 0208-512 was detected with a strong statistical significance ( 
) by EGRET [von Montigny et al. 1995a]. The high-confidence identification is
with a highly polarised quasar at a red shift of 1.003 [Savage 1976; Peterson et al. 1976; Impey & Tapia 1988]. PKS 0208-512 has had the hardest gamma-ray
spectrum of all EGRET sources, with a differential spectral index of
-1.69 
0.05 between 40 MeV and 30 GeV [Bertsch et al. 1993]. The five
observations in the first EGRET source catalog show clear evidence of
variability in the greater than 100 MeV gamma-ray flux by at least a factor of
three on time-scales of tens of days [Bertsch et al. 1993]. Similar variability behaviour was
also seen in phase II observations [von Montigny et al. 1995a], and in phase III, when it
was the brightest gamma-ray blazar observed by almost a factor of two (R. Hartman et al. 1995, private communication). Recently PKS 0208-512 underwent a major outburst in gamma-rays above the 100 MeV level, further confirming its variable behaviour [Vestrand et al. 1996].
Figure: Low contour, 1%. Peak, 2.1 Jy/beam. Beam, 1.9 
0.6 mas @ 8.0 
. N.B. For each image in this chapter the displayed contours range from the lowest contour indicated in the Figure captions to the highest contour, which is 64% of the peak flux density in the image, each contour increasing by a factor of two. Also, the beam dimensions are of the beam FWHM.
The compact nature of PKS 0208-512 was revealed in the 1982 SHEVE
observations at 2.3 GHz, as it was unresolved on the inner Australian
baselines [Preston et al. 1989]. The new VLBI observations at 4.8 GHz (Figure
4.1) show that the radio source consists of a bright, unresolved core
and a jet-like extension at a position angle of approximately
233 . It is estimated, from these data, that the compact
radio core has an observed brightness temperature of 
K, with a de-convolved FWHM of 
0.5 
mas and flux density
of 2.4 Jy at 4.8 GHz. This corresponds to a source frame brightness temperature of 
K, at or above the inverse Compton limit for
synchrotron radiation. The position angle of the jet-like feature in
Figure 4.1 aligns closely with a 5'' extension at a position angle of
219 seen with the Australia Telescope Compact Array (ATCA) at
4.8 GHz [Lovell, McCulloch, & Jauncey 1995]. The misalignment between the
mas-scale and arcsecond-scale structures is
14 .
Since only one epoch of high resolution VLBI data is available, any motion of the jet-like feature relative to the core cannot be estimated. The 1982 data of Preston et al. [1989] could be modelled by a single Gaussian component. However, the resolution of those observations is well below those reported here.