Nonthermal Radio Emission from Planetary Nebulae

In a recent analysis of the radio emission from the planetary nebula A30, Dgani, Evans & White (1998) claim that the emission, located in the inner region, is probably dominated by nonthermal emission. We propose a model to explain this. We assume that the fast wind, blown by the central star of A30 carries a very weak magnetic field. The interaction of this wind with a cluster of dense condensations traps the magnetic field lines for a long time and stretches them, leading to a strong magnetic field. If relativistic particles are formed as the fast wind is shocked, then the enhanced magnetic field will result in nonthermal radio emission. The typical nonthermal radio flux at 1 GHz can be up to several milli-Jansky. In order to detect the nonthermal emission, the emitting region should be spatially resolved from the main optical nebula. We list other planetary nebulae which may possess nonthermal radio emission.