Pulsar Magnetospheric Emission Mapping: Images and Implications of Polar-Cap Weather

The beautiful sequences of drifting'' subpulses observed in some radio pulsars have been regarded as among the most salient and potentially instructive characteristics of their emission, not least because they have appeared to represent a system of subbeams in motion within the emission zone of the star. Numerous studies of these drift’’ sequences have been published, and a model of their generation and motion articulated long ago by Ruderman & Sutherland (1975); but efforts thus far have failed to establish an illuminating connection between the drift phemomenon and the actual sites of radio emission. Through a detailed analysis of a nearly coherent sequence of drifting'' pulses from pulsar B0943+10, we have in fact identified a system of subbeams circulating around the magnetic axis of the star. A mapping technique, involving a cartographic’’ transform and its inverse, permits us to study the character of the polar-cap emission map'' and then to confirm that it, in turn, represents the observed pulse sequence. On this basis, we have been able to trace the physical origin of the drifting-subpulse’’ emission to a stably rotating and remarkably organized configuration of emission columns, in turn traceable possibly to the magnetic polar-cap ``gap’’ region envisioned by some theories.