2008ApJ...680..867K

In 1996 a major radio flux density outburst occurred in the broad-line radio galaxy 3C 111. It was followed by a particularly bright plasma ejection associated with a superluminal jet component, which has shaped the parsec-scale structure of 3C 111 for almost a decade. Here we present results from 18 epochs of Very Long Baseline Array (VLBA) observations conducted since 1995 as part of the VLBA 2 cm Survey and MOJAVE monitoring programs. This major event allows us to study a variety of processes associated with outbursts of radio-loud AGNs in much greater detail than has been possible in other cases: the primary perturbation gives rise to the formation of a leading and a following component, which are interpreted as a forward and a backward shock. Both components evolve in characteristically different ways and allow us to draw conclusions about the work flow of jet-production events; the expansion, acceleration and recollimation of the ejected jet plasma in an environment with steep pressure and density gradients are revealed; trailing components are formed in the wake of the primary perturbation, possibly as a result of coupling to Kelvin-Helmholtz instability pinching modes from the interaction of the jet with the external medium. The interaction of the jet with its ambient medium is further described by the linear-polarization signature of jet components traveling along the jet and passing a region of steep pressure/density gradients.