We report radio polarization observations of G319.9–0.7 ( MSC 319.9–0.7 ) at 3 and 6 cm obtained with the Australia Telescope Compact Array .
The source shows a highly elongated morphology with the energetic pulsar J1509–5850 located at the tip .
We found a flat radio spectrum of index \alpha = -0.26 \pm 0.04 and a high degree of linear polarization .
These results confirm G319.9–0.7 as a bow-shock pulsar wind nebula .
The polarization maps suggest a helical magnetic field trailing the pulsar , with the symmetry axis parallel to the system ’ s inferred direction of motion .
This is the first time such a field geometry has been seen in a bow-shock nebula , and it may be the result of an alignment between the pulsar spin axis and its space velocity .
Compared to other bow-shock examples , G319.9–0.7 exhibits very different properties in the field structure and surface brightness distribution , illustrating the large diversity of the population .