Drifting subpulses and inner acceleration regions in radio pulsars

TLDR: In this article, a more detailed analysis revealed that the circulation speed in a pure vacuum gap is too high when compared with observations, and some pul- sars demonstrate significant time variations of the drift rate, including a change of the apparent drift direction.

Abstract: The classical vacuum gap model of Ruderman & Sutherland, in which spark-associated subbeams of subpulse emission circulate around the magnetic axis due to the E × B drift of spark plasma filaments, provides a natural and plausible physical mechanism of the subpulse drift phenomenon. Moreover, this is the only model with quantitative predictions that can be compared with observa- tions. Recent progress in the analysis of drifting subpulses in pulsars has provided a strong support to this model by revealing a number of subbeams circulating around the magnetic axis in a manner compatible with theoretical predictions. However, a more detailed analysis revealed that the circulation speed in a pure vacuum gap is too high when compared with observations. Moreover, some pul- sars demonstrate significant time variations of the drift rate, including a change of the apparent drift direction, which is obviously inconsistent with the E × B drift scenario in a pure vacuum gap. We attempted to resolve these discrepancies by considering a partial flow of iron ions from the positively charged polar cap, co- existing with the production of outflowing electron-positron plasmas. The model of such charge-depleted acceleration region is highly sensitive to both the critical ion temperature Ti � 10 6 K (above which ions flow freely with the corotational charge density) and the actual surface temperature Ts of the polar cap, heated by the bombardment of ultra-relativistic charged particles. By fitting the obser- vationally deduced drift-rates to the theoretical values, we managed to estimate polar cap surface temperatures in a number of pulsars. The estimated surface temperatures Ts correspond to a small charge depletion of the order of a few percent of the Goldreich-Julian corotational charge density. Nevertheless, the re-