The structure of integrated pulse profiles

Abstract

We offer two possible explanations to account for the characteristics of integrated pulse profiles, in particular their degree of complexity, their variation from pulsar to pulsar, their stability, and the tendency of complex profiles to be associated with older pulsars. It is proposed that the pulse structure could be a reflection of surface irregularities at the polar caps, and it is shown how the surface relief can affect the number of positrons released into the magnetosphere which are subsequently responsible for the observed radio radiation. The electrons produced in the vacuum break-down in the gap carry enough energy to allow creating such a surface relief in ~ 10-6 years, and one way in which this could be achieved is discussed. Alternatively, the presence of multi pole components in the magnetic fields of older pulsars could lead to significant variations in the curvature of the field lines across the gap, and hence to structure in the integrated pulse profiles. An assessment of the two hypotheses from observed pulse profiles seems to favour the polar cap relief picture.