Evolution of the Parsec-scale Structure of PKS 1934-638 Revisited: First Science with the ASKAP and New Zealand Telescopes
2010
We have studied the archetypal Gigahertz Peaked Spectrum radio galaxy, PKS 1934−638, using the Australian
Long Baseline Array augmented with two new telescopes that greatly improve the angular resolution of the array.
These very long baseline interferometry observations represent the first scientific results from a new antenna in New
Zealand and the first antenna of the Australian SKA Pathfinder. A compact double radio source, PKS 1934−638
has been monitored over a period of 40 years and the observation described here provides the latest datum, eight
years after the previous observation, to aid in the study of the long-term evolution of the source structure. We take
advantage of these new long baselines to probe PKS 1934−638 at the relatively low frequency of 1.4 GHz in order
to examine the effects of optical depth on the structure of the radio source. Optical depth effects, resulting in the
observation of frequency-dependent structure, may have previously been interpreted in terms of an expansion of the
source as a function of time. Expansion and frequency-dependent effects are important to disentangle in order to
estimate the age of PKS 1934−638. We show that frequency-dependent structure effects are likely to be important
in PKS 1934−638 and present a simple two-dimensional synchrotron source model in which opacity effects due
to synchrotron self-absorption are taken into account. Evidence for expansion of the radio source over 40 years is
therefore weak with consequences for the estimated age of the radio source.
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