Unusual evolutionary features and complicated characteristics of drifting subpulses have been observed in some pulsars (Wright & Fowler 1981; Smits et al., 2005; Basu & Mitra 2018), described in terms of multiple subpulse drift rates, presenting difficulties to the traditional understanding of the phenomenon. The observations strongly suggest that multiple quasi-stable emission states are allowed and that the pulsar can jump abruptly between different states demonstrated as different subpulse drift modes each associates uniquely with a drift rate to a state. It is rather puzzling as to how pulsars with similar properties while some can display such diversity in subpulse drift mode features. It is expected that multiple drift modes and switching can provide unparallel opportunity to probe deeper into the magnetosphere to reveal useful information for the physical properties of pulsar radio emission and its sporadic properties. However, our current understanding of the phenomena is poor and limited tools exist for revealing the mechanism that gives rise to different drift modes.

In this work, 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 as seen by an observer, and switching in drift mode corresponds to an abrupt jump in the magnetospheric state causing variation in the plasma flow. We demonstrate that changes in drift rate occur both as functions of pulsar rotational phase and the magnetospheric state, 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.

Author: Rai Yuen, Associate Researcher

Publication: R. Yuen, 2019, MNRAS, 486, 2011 

References:

Wright G. A. E., Fowler L. A., 1981, A&A., 101, 356

Smits J. M., Mitra D., Kuijpers J., 2005, A&A, 440, 683

Basu R., Mitra D., 2018, MNRAS, 476, 1345