Parsec-scale jet in the distant gigahertz-peaked spectrum quasar PKS 0858–279

The high redshift GPS quasar PKS 0858–279 exhibits the following properties which make the source unusual. Our RATAN-600 monitoring of 1–22 GHz spectrum has detected broad-band radio variability with high amplitude and relatively short time scale. In the same time, the milliarcsecond scale structure observed in a snapshot VLBA survey turned out to be very resolved which is not expected from the fast flux density variations. We performed 1.4–22 GHz VLBA observations of this quasar in 2005–2007. It has revealed a core-jet morphology. A high Doppler factor δ is suggested for the jet, its nature is discussed in this report on the basis of the multi-frequency VLBA and RATAN data collected. Synchrotron self-absorption was confirmed to be dominating at low frequencies, the magnetic field strength of the dominating jet feature is estimated of an order of 0.1δ mG (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)