MeerKAT observations of pair-plasma induced birefringence in the double pulsar eclipses

TL;DR

This study uses MeerKAT radio observations to analyze how pair-plasma in pulsar B's magnetosphere causes birefringence effects during eclipses of pulsar A, revealing detailed magnetic geometry.

Contribution

First detailed polarization analysis of double pulsar eclipses linking birefringence effects to the magnetospheric plasma and magnetic field geometry.

Findings

Eclipses cause significant circular polarization and rapid linear polarization changes.

Synchrotron absorption in pair-plasma explains observed polarization behaviors.

Magnetic field geometry of pulsar B is unambiguously determined.

Abstract

PSR J0737$-$3039A/B is unique among double neutron star systems. Its near-perfect edge-on orbit causes the fast spinning pulsar A to be eclipsed by the magnetic field of the slow spinning pulsar B. Using high-sensitivity MeerKAT radio observations combined with updated constraints on the system geometry, we studied the impact of these eclipses on the incident polarization properties of pulsar A. Averaging light curves together after correcting for the rotation of pulsar B revealed enormous amounts of circular polarization and rapid changes in the linear polarization position angle, which occur at phases where emission from pulsar A is partially transmitted through the magnetosphere of pulsar B. These behaviours confirm that the eclipse mechanism is the result of synchrotron absorption in a relativistic pair-plasma confined to the closed-field region of pulsar B's truncated dipolar magnetic field. We demonstrate that changes in circular polarization handedness throughout the eclipses are directly tied to the average line of sight magnetic field direction of pulsar B, from which we unambiguously determine the complete magnetic and viewing geometry of the pulsar.