Properties of the emission region in pulsars with opposite subpulse drift directions in different profile components

TL;DR

This paper models pulsar emission regions using a rotating carousel framework to explain opposite subpulse drift directions and their coexistence, revealing that different emission states can occur simultaneously and vary across the emission region.

Contribution

It introduces a model linking subpulse drift directions to emission states and parameters, explaining the coexistence of opposite drifts in pulsars.

Findings

Different drift directions correspond to specific emission states and parameters.

Emission states can coexist and operate concurrently in a pulsar's emission region.

Subpulse arrangement varies across the emission region, indicating non-uniformity.

Abstract

We investigate properties of the emission region as revealed by drifting subpulses of opposite drift directions at different parts of a pulse profile by using the rotating carousel model in an obliquely rotating pulsar magnetosphere of multiple emission states. Subpulse emission is assumed coming from m discrete emission areas that are distributed around the magnetic axis on a rotating carousel. The flow rate of the emission areas is determined by the E x B drift in an emission state, designated by the parameter y, in which E and the associated flow rate are dependent on y. In this model, subpulses appear to drift in an emission state if a relative speed exists between the plasma flow and corotation, and the diversity in the drift rates and directions corresponds to the relative speed being different in different parts of a profile. We apply the model to three pulsars that exhibit drifting subpulses of opposite drift directions to identify the emission states and the values of m. Our results show that different drifting subpulses correspond to particular values of m and y, and the latter implies that different emission states can coexist and operate concurrently in an emission region. We find that m does not show clear dependency on either the obliquity angle or emission state. We demonstrate that subpulse arrangement may vary across an emission region meaning that it is not always uniform on a carousel. We discuss drifting subpulses of opposite drift directions and subpulse drift-rate switching in terms of different emission states in our model, and speculate that they may be two manifestations of the same underlying mechanism.