WSRT AND VLA OBSERVATIONS OF THE RADIO GALAXY B2 0326 + 39 AT 0.6, 1.5 AND 5 GHZ

The radio galaxy B20326 + 39 has been imaged with the WSRT and the VLA at 0.6, 1.5 and 5 GHz, with angular resolutions from 26" to 0".3. The radio source contains an unresolved opaque radio core that is linked by two jets to broad lobes with faint S-symmetric elongations. The west jet is marginally brighter than the east jet on the large scale but is much brighter for the first 4 kpc from the core. The transition from "one-sided" to "two-sided" intensity symmetry between the jets is accompanied by a change in the apparent magnetic field direction on the jet axis from dominantly parallel to dominantly perpendicular to the jet. The jets do not spread (i.e., expand laterally) at a constant rate, but alternate between slow and rapid spreading. They also contain regions with both adiabatic and sub-adiabatic intensity-radius variations within 10 kpc of the core. The regions of most rapid spreading are those where the central intensity declines most slowly with increasing jet radius. The jets do not share the S-symmetry of the outer steep-spectrum extensions of the lobes - the west jet has a much more pronounced "wiggle" as it enters its lobe. The spectral index of the west jet decreases by about 0.3, and the jet brightens, near an extremity of this "wiggle". The "wiggling" may therefore be related to a change in the internal structure of the jet that also stimulates relativistic particle (re)acceleration in this region. There is evidence for a Faraday rotation measure gradient across the source, perhaps as large as 40-60 rad m-2. We cannot be certain whether this gradient is intrinsic to the source or is a property of the foreground magnetoionic medium of our galaxy. We consider various ways to estimate the Mach number and velocity of the jets. A consistent picture of the lobe energetics, jet morphology, and the polarisation properties of the jet can be found. In this picture, the jets are initially light, confined and mildly supersonic but are decelerated and become denser as they propagate away from the core. It is unlikely that the lobes have come to radiative equilibrium with the energy flux provided by the jets.