A Mechanism of Spark Motion in Inner Acceleration Region to Investigate Subpulse Drifting in Pulsars

TL;DR

This paper models subpulse drifting in pulsars by simulating spark dynamics in a non-dipolar inner acceleration region, explaining various observed drifting behaviors through the lagging sparks concept.

Contribution

It introduces a simulation framework for pulsar subpulse drifting based on spark lagging in a non-dipolar magnetic field environment, advancing understanding of pulsar emission mechanisms.

Findings

Reproduces different drifting phase behaviors with simple spark lag assumptions.

Shows drifting periodicity remains constant across profile components.

Supports the non-dipolar magnetic field model in pulsar inner regions.

Abstract

Coherent radio emission in pulsars is excited due to instabilities in a relativistically streaming non-stationary plasma flow, which is generated from sparking discharges in the inner acceleration region (IAR) near the stellar surface. A number of detailed works have shown the IAR to be a partially screened gap (PSG) dominated by non-dipolar magnetic fields with continuous outflow of ions from the surface. The phenomenon of subpulse drifting is expected to originate due to variable $\mathbf{E}\times\mathbf{B}$ drift of the sparks in PSG, where the sparks lag behind corotation velocity of the pulsar. Detailed observations show a wide variety of subpulse drifting behaviour where subpulses in different components of the profile have different phase trajectories. But the drifting periodicity is seen to be constant, within measurement errors, across all components of the profile. Using the concept of sparks lagging behind corotation speed in PSG as well as the different orientations of the surface non-dipolar magnetic fields we have simulated the expected single pulse behaviour in a representative sample of pulsars. Our results show that the different types of drifting phase behaviour can be reproduced using these simple assumptions of spark dynamics in a non-dipolar IAR.