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3C84 (NGC1275) is one of the brightest radio sources in the mm radio-bands,which led to a plethora of VLBI observations at numerous frequencies over theyears. They reveal a two-sided jet structure, with an expanding but notwell-collimated parsec-scale jet, pointing southward. High resolution mm-VLBIobservations allow the study and imaging of the jet base on the sub-parsecscale. This could facilitate the investigation of the nature of the jet origin,also in view of the previously detected two-railed jet structure and east-westoriented core region seen with RadioAstron at 22 GHz. We produce VLBI images ofthis core and inner jet region, observed during the past twenty years at 15,43, and 86 GHz. We determine the kinematics of the inner jet and ejectedfeatures at 43 and 86 GHz and compare their ejection times with radio and$\gamma$-ray variability. For the moving jet features, we find an averagevelocity of $\beta^\textrm{avg}_\textrm{app} = 0.055-0.22$c ($\mu^\textrm{avg}= 0.04-0.18\,$mas/yr). From the time-averaged VLBI images at the threefrequencies, we measure the transverse jet width along the bulk flow. On the$\leq 1.5$ parsec scale, we find a clear trend of the jet width being frequencydependent, with the jet being narrower at higher frequencies. Thisstratification is discussed in the context of a spine-sheath scenario, and iscompared to other possible interpretations. From quasi-simultaneousobservations at 43 and 86\,GHz we obtain spectral index maps, revealing atime-variable orientation of the spectral index gradient, due to structuralvariability of the inner jet.

Jet kinematics in the transversely stratified jet of 3C 84 A two-decade overview