The double pulsar: evidence for neutron star formation without an iron core-collapse supernova

TL;DR

This paper presents evidence that the second neutron star in the double pulsar system was formed through a symmetric process, likely electron-capture supernova, challenging the typical core-collapse supernova model.

Contribution

The study provides detailed observational constraints on the system geometry, supporting a neutron star formation scenario without an iron core-collapse supernova.

Findings

The recycled pulsar is a near-orthogonal rotator with a 90-degree separation between spin and magnetic axes.

The misalignment between the pulsar's spin and orbital axes is constrained to less than 3.2 degrees.

The second neutron star likely formed via a symmetric electron-capture supernova.

Abstract

The double pulsar system PSR J0737-3039A/B is a double neutron star binary, with a 2.4-hour orbital period, which has allowed measurement of relativistic orbital perturbations to high precision. The low mass of the second-formed neutron star, as well as the low system eccentricity and proper motion, point to a different evolutionary scenario compared to most other known double neutron star systems. We describe analysis of the pulse profile shape over 6 years of observations, and present the resulting constraints on the system geometry. We find the recycled pulsar in this system, PSR J0737-3039A, to be a near-orthogonal rotator, with an average separation between its spin and magnetic axes of 90 +/- 11 +/- 5 deg. Furthermore, we find a mean 95% upper limit on the misalignment between its spin and orbital angular momentum axes of 3.2 deg, assuming that the observed emission comes from both magnetic poles. This tight constraint lends credence to the idea that the supernova that formed the second pulsar was relatively symmetric, possibly involving electron-capture onto an O-Ne-Mg core.