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

Abstract

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 the years. They reveal a two-sided jet structure, with an expanding but not well-collimated parsec-scale jet, pointing southward. High resolution mm-VLBI observations allow the study and imaging of the jet base on the sub-parsec scale. 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-west oriented core region seen with RadioAstron at 22 GHz. We produce VLBI images of this 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 ejected features at 43 and 86 GHz and compare their ejection times with radio and $\gamma$-ray variability. For the moving jet features, we find an average velocity of ${\beta }_{\text{app}}^{\text{avg}}=0.055-0.22$c (${\mu }^{\text{avg}}=0.04-0.18$mas/yr). From the time-averaged VLBI images at the three frequencies, we measure the transverse jet width along the bulk flow. On the $\le 1.5$ parsec scale, we find a clear trend of the jet width being frequency dependent, with the jet being narrower at higher frequencies. This stratification is discussed in the context of a spine-sheath scenario, and is compared to other possible interpretations. From quasi-simultaneous observations at 43 and 86\,GHz we obtain spectral index maps, revealing a time-variable orientation of the spectral index gradient, due to structural variability of the inner jet.

23 pages, 12 figures, accepted for publication in A&A

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Cited by in corpus (9)

• Ordered magnetic fields around the 3C 84 central black hole
• A multiband study and exploration of the radio wave - $\gamma$-ray connection in 3C 84
• Evidence for a toroidal magnetic field in the core of 3C 84
• Observational Evidence to Support a Dense Ambient Medium Shaping the Jet in 3C 84
• First VLBI detection of Fornax A
• Evolution, speed, and precession of the parsec-scale jet in the 3C 84 radio galaxy
• Detection of an orthogonal alignment between parsec scale AGN jets and their host galaxies
• Where within the 3C 84 jet are $\gamma$-rays produced?
• Detection of Compton scattering in the jet of 3C 84