INTRINSIC EVOLUTION OF A SUPERLUMINAL KNOT IN 3C-345

In the quasar 3C 345 jet components move superluminally along bent tra jectories, which differ for each component. Qian et al., (1991) & (199 2) derived a geometric helical motion model for the jet components C4 & C5. From this helical geometry and the observed motion, the time-dep endence of the Doppler boosting factor is derived and used to relativi stically correct the observed flux density and size variability of C4. Very different from the observed behaviour and not consistent with ex pectations from canonical models, the intrinsic (Doppler-corrected) fl ux density evolution of C4 shows a nearly rectangular outburst-like sh ape with rising and decay times of similar to 5 - 10 yrs in the comovi ng frame. At the same time C4 expands subluminally with an intrinsic v elocity of upsilon(int) similar to 0.09 c. Both, variability and sublu minal expansion, are discussed in a model involving field amplificatio n and 'in situ' particle acceleration followed by adiabatic expansion.