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Session 118 - Radiogalaxies.
Oral session, Thursday, January 16
Harbour A,
Multiconfiguration VLA images of the bright, nearby radio galaxy 3C 353 at five frequencies show a resolved (up to 9 0\farcs44 FWHM beamwidths across) jet, counterjet, and numerous high-contrast filaments. The jets contain \sim 1% of the source's flux density at 4.9 GHz, are well-collimated and typically have a flat-topped transverse total intensity profile. The jets appear only weakly linearly polarized but have striking minima in both polarized intensity and degree of linear polarization near their edges. The minima are interpreted as the result of vector cancelation of polarized emission in the outer portions of the jet and ambient emission. The magnetic field in the ambient material is predominantly perpendicular to the jet axis; thus, it is inferred that the jet emission responsible for the polarization minima has a magnetic field whose dominant component in projection is parallel to the jet axis. A simple model for the magnetic field organization and emissivity distribution predicts transverse total and polarized intensity profiles consistent with those of the jet and counterjet. Both jets consist of an outer layer that is approximately one half the jet radius and contains only random axial and azimuthal components of approximately equal magnitudes and an inner spine with an emissivity \leq \frac12 that of the outer layer; additionally, the model implies that the jet axis lies \leq 30\deg to the plane of the sky. The absence of a radial magnetic field component in the outer layer strongly suggests a boundary layer where the magnetic field is ordered by a velocity gradient. Although there are several plausible mechanisms for reducing the emissivity of the spine, Doppler hiding due to bulk relativistic motion is attractive as it suggests a way to unify our picture of 3C 353 with FR I and quasar jets.
