Radio Study of the Pulsar Wind Nebula Powered by PSR B1706-44

PSR B1706$-$44 is an energetic gamma-ray pulsar located inside supernova remnant (SNR) G343.1$-$2.3 and it powers a compact pulsar wind nebula (PWN) that shows torus and jet structure in X-rays. We present a radio study of the PWN using Australia Telescope Compact Array (ATCA) observations at 3, 6, 13, and 21\,cm. We found an overall arc-like morphology at 3 and 6\,cm, and the ``arc" shows two distinct peaks at 6\,cm. The radio emission is faint inside the X-ray PWN and only brightens beyond that. We develop a thick torus model with Doppler boosting effect to explain the radio PWN structure. The model suggests a bulk flow speed of $\sim 0.2c$, which could indicate significant deceleration of the flow from the X-ray emitting region. Our polarization result reveals a highly ordered toroidal $B$-field in the PWN. Its origin is unclear given that the supernova reverse shock should have interacted with the PWN. At a larger scale, the 13 and 21\,cm radio images detected a semi-circular rim and an east-west ridge of G343.1$-$2.3. We argue that the latter could possibly be a pulsar tail rather than a filament of the SNR, as supported by the flat radio spectrum and the alignment between the magnetic field and its elongation.