Competing Drifting Radio Subpulses in PSR B0031-07

The pair of drifting subpulses of the radio pulsar PSR B0031-07 appear to be well separated from each other on the average, overlapping at less than one thirtieth of the peak energy. Strictly, the integrated profile of the pair (after removing the drift) does not show more than two subpulses; however this result is likely to be modified with the availability of more data. On the other hand, rare instances of three simultaneous subpulses in a single period have been noticed. This is consistent with the Ruderman and Sutherland model of the drifting phenomenon in which several sparks, uniformly spaced on a circle, rotate around the polar cap. The third subpulse appears to show up strongly when subpulses belonging to the primary drift bands weaken. Although this conclusion is based mainly on two reliable examples, it suggests an anti correlation of the subpulse energies. The normalised correlation coefficient between the energies of the two subpulses in a period is -0.16 +- 0.02, after accounting for a known selection effect. Simulations suggest that this result could not be an artefact. This suggests the idea of competing drifting subpulses which, if true, will have important ramifications for the growth and breakdown of the particle acceleration zones in pulsars.