Multi - frequency investigation of the parsec - and kilo - parsec - scale radio structures in high - redshift quasar PKS 1402 + 044

Aims. 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. Methods. The observational data were obtained with the VLBI Space Observatory Programme (VSOP) at 1.6 and 5 GHz, supplemented by other multi-frequency observations with the The observations span a period of 7 years. Results. 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 ∼ 10 9 M ⊙. The upper limit of the jet proper motion of PKS 1402+044 is 0.03 mas yr −1 (∼ 3c) in the east-west direction.