Drifting, moding, and nulling: another look at pulsar B1918+19

TL;DR

This study provides a detailed analysis of pulsar B1918+19's subpulse behavior, revealing multiple drift modes, nulling patterns, and a potential common circulation time linked to E×B drift, offering insights into pulsar emission dynamics.

Contribution

It introduces a unified model explaining the drift modes, nulling, and subbeam behavior, suggesting aliasing and subbeam loss as key factors in pulsar emission variability.

Findings

Identified three distinct drift modes and a disordered mode with specific cycle patterns.

Nulls are mainly confined to certain modes and show quasi-periodic behavior.

All drift modes share a common circulation time of about 12 pulsar periods.

Abstract

Arecibo observations of the conal triple pulsar B1918+19 at 0.327- and 1.4-GHz are used to analyse its subpulse behaviour in detail. We confirm the presence of three distinct drift modes (A,B,C) plus a disordered mode (N) and show that they follow one another in specific cycles. Interpreting the pulsar's profile as resulting from a sightline traverse which cuts across an outer cone and tangentially grazes an inner cone, we demonstrate that the phase modulation of the inner cone is locked to the amplitude modulation of the outer cone in all the drift modes. The 9% nulls are found to be largely confined to the dominant B and N modes, and, in the N mode, create alternating bunches of nulls and emission in a quasi-periodic manner with an averaged fluctuation rate of about 12 rotation periods ($P_1$). We explore the assumption that the apparent drift is the first alias of a faster drift of subbeams equally spaced around the cones. This is shown to imply that all modes A, B and C have a common circulation time of 12 $P_1$ and differ only in the number of subbeams. This timescale is on the same order as predicted by the classic {\bf E}$\times${\bf B} drift and also coincides with the N-mode modulation. We therefore arrive at a picture where the circulation speed remains roughly invariant while the subbeams progressively diminish in number from modes A to B to C, and are then re-established during the N mode. We suggest that aliasing combined with subbeam loss may be responsible for apparently dramatic changes in drift rates in other pulsars.