Polarised views of the drifting subpulse phenomenon

Abstract

I review recent results concerning the shape of drifting subpulse patterns, and the relationship to model predictions. While a variety of theoretical models exist for drifting subpulses, observers typically think in terms of a spatio-temporal model of circulating beamlets. Assuming the model is correct, geometric parameters have been inferred and animated "maps" of the beam have been made. However, the model makes very specific predictions about the curvature of the drift bands that have remained largely untested. Work so far in this area indicates that drift bands tend not to follow the prediction, and in some cases discontinuities are seen that are suggestive of the superposition of out of phase drift patterns. Recent polarimetric observations also show that the drift patterns in the two orthogonal polarisation modes are offset in phase. In one case the pattern in one of the modes shows a discontinuity suggesting no less than three superposed, out-of-phase drift patterns! I advise caution in the interpretation of observational data in the context of overly simplistic models.