Extreme jet bending on kiloparsec scales: the 'doughnut' in NGC 6109

We present new radio observations of the z = 0.029 radio galaxy NGC 6109, a member of the 3CRR sample. We find the radio morphology of the counter-jet to be highly distorted, showing a unique 'doughnut' structure ~6 kpc in diameter. The doughnut is overpressured compared with the surrounding atmosphere as measured with Chandra. We investigate the polarisation properties of the source and find evidence for an interaction between the doughnut and the external environment. This may cause the extreme jet bend. Alternatively, while providing no explanation for the rotation-measure and magnetic field structure seen in the doughnut, a ballistic precession model may be feasible if the ballistic flow persists for a distance much less than the full extent of the 100 kpc-scale jet. A light jet being deflected by gas flows and winds just outside the transition between the galaxy and cluster atmospheres appears to be a more plausible interpretation.