(a) constant (5000:1) dynamic range and
(b) constant sensitivity.
The relativistic jet model used to generate these displays is the best fit to 8 GHz VLA data for 3C31 at 0.25 arcsec resolution by R.A.Laing and A.H.Bridle (2002: MNRAS, 336, 328). This best fit occurs for an angle of 52 degrees between the jet and the line of sight. The inner region contains a jet with fast (0.8 -- 0.9c) outflow on the axis and much slower flow at its edge. A discontinuity in the flow then occurs at which the jet flares and its emissivity increases suddenly. The on-axis velocity stays fairly constant at approximately 0.8c until the end of the flaring region, where it drops abruptly to approximately 0.55c. The velocity then slowly decreases to approximately 0.25c at the end of the modelled region. Throughout the flaring and outer regions, the velocity at the edge of the jet is approximately 0.7 of its on-axis value. The magnetic field in the flaring region is complex, with an essentially isotropic structure at the edge of the jet, but a more ordered toroidal+longitudinal configuration on-axis. In the outer region, the radial field vanishes and the toroidal component becomes dominant.
The discontinuity between the inner and flaring regions can be associated with a stationary shock structure. The inferred transverse velocity profiles and field structure in the flaring region support the idea that the jets decelerate by entraining the external medium from the galactic atmosphere of 3C31.
The "constant-sensitivity" displays show what would be seen by an ideal radio telescope that could detect the faintest levels of emission equally no matter how bright the compact central component becomes due to relativistic beaming.
The "constant-dynamic-range" displays correspond better to standard radio astronomical observations that have not been specially optimized to detect the faintest broad features in the presence of strong compact features..
The jets appear identical when observed in the plane of the sky (90 degrees to the line of sight), as at the start of each animation.
The animations illustrate how, at angles closer to the line of sight,
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