A MeerKAT view of the double pulsar eclipses -- Geodetic precession of pulsar B and system geometry

Abstract

The double pulsar system, PSR J0737$-$3039A/B, consists of two neutron stars bound together in a highly relativistic orbit that is viewed nearly edge-on from the Earth. This alignment results in brief radio eclipses of the fast-rotating pulsar A when it passes behind the toroidal magnetosphere of the slow-rotating pulsar B. The morphology of these eclipses is strongly dependent on the geometric orientation and rotation phase of pulsar B, and their time-evolution can be used to constrain the geodetic precession rate of the pulsar. We demonstrate a Bayesian inference framework for modelling eclipse light-curves obtained with MeerKAT between 2019-2023. Using a hierarchical inference approach, we obtained a precession rate of ${\Omega }_{\mathrm{SO}}^{\mathrm{B}}={5.16^{\circ }}_{-0.34^{\circ }}^{+0.32^{\circ }}$ yr${}^{-1}$ for pulsar B, consistent with predictions from General Relativity to a relative uncertainty of 6.5%. This updated measurement provides a 6.1% test of relativistic spin-orbit coupling in the strong-field regime. We show that a simultaneous fit to all of our observed eclipses can in principle return a $\sim$1.5% test of spin-orbit coupling. However, systematic effects introduced by the current geometric orientation of pulsar B along with inconsistencies between the observed and predicted eclipse light curves result in difficult to quantify uncertainties. Assuming the validity of General Relativity, we definitively show that the spin-axis of pulsar B is misaligned from the total angular momentum vector by $40.6^{\circ }\pm 0.1^{\circ }$ and that the orbit of the system is inclined by approximately $90.5^{\circ }$ from the direction of our line of sight. Our measured geometry for pulsar B suggests the largely empty emission cone contains an elongated horseshoe shaped beam centered on the magnetic axis, and that it may not be re-detected as a radio pulsar until early-2035.

Abridged abstract. 13 pages, 9 figures and 2 tables

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• The Relativistic Spin Precession in the Compact Double Neutron Star System PSR~J1946+2052
• Tackling artefacts in the timing of relativistic pulsar binaries: towards the SKA
• Nethotrons: exploring the possibility of measuring relativistic spin precessions, from Earth's satellites to the Galactic Centre