THE PARSEC-SCALE RADIO JET OF 4C 39.25

Previous VLBI observations of the peculiar superluminal quasar 4C 39.25 at wavelengths lambda = 1.3, 2.8, and 3.6 cm have revealed the presence of a superluminal component (b) moving between the western component (c) and the eastern component (a). Here we combine data published previously and reanalyzed by us with new VLBI observations between 1986 and 1989 at these wavelengths. Components a and c have remained fixed relative to each other, while component b has slowed down and brightened as it approaches component a. Our most recent lambda = 1.3 cm VLBI observations have revealed the presence of a fourth, weak component (d) (to the west of c), which could be the core of the radio source, undetected in previous observations presumably due to an inverted spectrum and the limited dynamic ranges of the older maps. These observational results support a model in which 4C 39.25 contains a bent relativistic jet which is misaligned relative to the observer near the core region, leading to a relatively low core brightness. Near the stationary components c and a, the jet curves its trajectory toward the observer, so as to become more closely aligned to the line of sight, while it is misaligned in the region between these two hotspots. We interpret component b as a shock wave propagating down the jet. This shock-in-curved-jet hypothesis is supported by the nonuniform proper motion of component b, the total and polarized flux density evolution of both the individual components and the source as a whole, the spectral evolution, and the relative position angles between the source components.