Radio-frequency microstructure and polarization in ion–proton pulsars

Abstract

It is shown that the time-variability inherent in the ion-proton polar cap leads naturally to growth of Langmuir modes on narrow bundles of magnetic flux lines and that the observed size of micropulses is consistent with the smallest such bundle that can plausibly support the growth of the modes. The polarization of integrated pulse profiles is revisited, specifically, the π/2 position-angle jumps that are frequently observed accompanied by a zero in polarization. The fact that radiation emitted above ion-proton polar caps is not tangential to the local flux lines but has a finite angular distribution proves to be the essence of understanding this phenomenon as is a constraint on the shape of the polar cap. In principle, the behaviour should also be seen if the form of the polar-cap ion-proton area in a single pulse satisfies certain conditions which are explained here.