Dual-frequency VSOP Imaging of a High-redshift Radio Quasar PKS 1402+044
  Based on the VLBI Space Observatory Programme (VSOP) observations at 1.6 and 5 GHz, we find that the luminous high-redshift (z=3.215) quasar PKS 1402+044 (J1405+0415) has a pronounced 'core--jet' structure. The jet shows a steeper spectral index and lower brightness temperature with the increase of the distance from the core. The variation of brightness temperature is basically consistent 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_sun. The upper limit of the jet proper motion of PKS 1402+044 is 0.03 mas/yr (~3c) in the east-west direction. 
Jun Yang (1 and 6), Leonid Gurvits (2), Andrei Lobanov (3), Sandor   Frey (4 and 5) and Xiao-Yu Hong (1) ((1) Shanghai Astro...