2008A&A...489..517Y

We investigate the frequency-dependent radio properties of the jet of the luminous high-redshift (z=3.2) radio quasar PKS 1402+044 (J1405+0415) by means of radio interferometric observations. The observational data were obtained with the VLBI Space Observatory Programme (VSOP) at 1.6 and 5GHz, supplemented by other multi-frequency observations with the Very Long Baseline Array (VLBA; 2.3, 8.4, and 15GHz) and the Very Large Array (VLA; 1.4, 5, 15, and 43GHz). The observations span a period of 7 years. We find that the luminous high-redshift quasar PKS 1402+044 has a pronounced ``core-jet'' morphology from the parsec to the kilo-parsec scales. The jet shows a steeper spectral index and lower brightness temperature with increasing distance from the jet core. The variation of brightness temperature agrees well with the shock-in-jet model. Assuming that the jet is collimated by the ambient magnetic field, we estimate the mass of the central object as ∼10⁹M_☉. The upper limit of the jet proper motion of PKS 1402+044 is 0.03mas/yr (∼3c) in the east-west direction.