Observations of drifting subpulses and their implications on models of pulsars

Abstract

Though both the polar cap and the relativistic beaming models explain the basic phenomenon of drifting subpulses, we show that the two models predict different tracks for subpulses in the longitude versus pulse-number diagram. Since this offers us a means of distinguishing between the two models we have used the Ooty radio telescope to observe PSR 0031 – 07, which shows strong drifting-subpulse behaviour. The observed dependence of the slope of subpulse bands on the longitude of the subpulse agrees better with the prediction of the relativistic beaming model than that of the polar cap model. We also show that the known subpulse behaviour of a few other pulsars also agrees with what is expected from the relativistic beaming model. The predictions of the polar cap model can be made compatible with the observations only if a clear physical basis is found for the speeds of the subpulse-producing sparks to depend on their position on the polar cap.