2019MNRAS.486.2011Y

We explore changes in subpulse drift rate in a model for pulsar magnetospheres of multiple magnetospheric states incorporating the apparent motion of the visible point. In this model, subpulse drift rate is determined by the relative motion between corotation and the plasma flow in a magnetospheric state, designated by the parameter y, as seen by an observer, and switching in drift mode corresponds to an abrupt jump in y causing variation in the plasma flow. We demonstrate that changes in drift rate occur both as functions of pulsar rotational phase and y, and that subpulses may appear stationary even when the plasma flow is not in corotation with the star. Our results suggest that pulsars with multiple subpulse drift modes may constitute a much larger population. We consider the different subpulse drift rates in PSRs J1822 - 2256, B0809+74 and B1918+19 as examples to illustrate that each drift mode corresponds to a unique magnetospheric state, and we discuss its implication in relation to the charge density as revealed by the value of y.