The Wikipedia linked in these comments says it is likely from electron precipitation. Basically the magnetic field traps free elections and thus “wiggles” as they interact with the field. This can make a (pulsed) radio jet shooting from the pole, which is how this planet was observed. These electrons can fine from atmospheric phenomena such as lightning or large storms.

Earth has the same but much weaker phenomenon, the Van Allen belt, which was a difficult challenge to handle in the early days of space exploration.