The blazar PKS 0537-441 (z=0.894) was detected with a strong
statistical significance by EGRET [von Montigny et al. 1995a] and subsequently became
a high-confidence identification. Its optical polarisation of
10 
[Impey & Tapia 1990] and optical variability with a total range of more
than 4 mag. (see references in Tanzi et al. 1986) is
reminiscent of BL Lac objects, but its broad optical emission lines
are features of quasars. It is sometimes classified as a highly
polarised quasar [Treves et al. 1993; Sambruna et al. 1994].
Figure: Low contour, 
1%. Peak, 3.0 Jy/beam. Beam, 1.8 
0.9 mas @ 4.5 
.
Figure: Low contour, 0.5%. Peak, 6.2 Jy/beam. Beam, 7.4 2.9 mas @ -87.8 .
The compact nature of PKS 0537-441 was clear from the 1982 SHEVE
observations at 2.3 GHz in which the object was unresolved on all
Australian baselines [Preston et al. 1989]. Using a 4 hr scan on the
intercontinental baseline from Australia to South Africa, along with
the shorter internal Australian baselines, [Preston et al. 1989] modelled the source as
a circular Gaussian component of 1.1 mas FWHM and total flux 4.2 Jy
with no evidence of a jet. The new VLBI images at 4.8 and 8.4 GHz
(Figures 4.8 and 4.9) show that the source is dominated by a slightly
resolved component which can be identified as the core, together with a
jet-like component extending towards the north at a position angle of
3 . The jet-like component may have appeared during the 10 years
between epochs, but it is just as likely that the lack of u-v
constraints in 1982 allowed the available data to be modelled with a
single component.
Perley [1982] found a 7.''2 extension to the compact radio core at a
position angle of 305 with the VLA. Thus, the misalignment
between the mas-scale and arcsecond-scale structures is
approximately 58 .
From Figure 4.8, the FWHM of the slightly resolved core component
is estimated to be, de-convolved from the beam, 0.9 0.3 mas with a
flux density of 4.0 Jy, from which an observed brightness
temperature is approximately 
K at 4.8 GHz can be inferred. The source frame brightness temperature is therefore approximately 
K, near the inverse Compton limit for synchrotron radiation.