Pulsar Spin-Velocity Alignment: Kinematic Ages, Birth Periods and Braking Indices

TL;DR

This study examines how pulsar spin-velocity alignment depends on age, using kinematic ages derived from proper motions, revealing that alignment diminishes after 10 million years and exploring implications for pulsar birth properties and supernova mechanisms.

Contribution

It provides the largest set of independently estimated pulsar ages and analyzes the evolution of spin-velocity alignment with these ages, offering new insights into pulsar birth and evolution.

Findings

Strong alignment in young pulsars diminishes after 10 Myr

Kinematic ages are crucial for understanding pulsar evolution

Implications for supernova kick mechanisms and pulsar birth properties

Abstract

This paper presents a detailed investigation of the dependence of pulsar spin-velocity alignment, which has been observed for a sample of 58 pulsars, on pulsar age. At first, our study considers only pulsar characteristic ages, resulting in no change in the degree of correlation as a function of age, up to at least 100 Myr. Subsequently, we consider a more reliable estimate of pulsar age, the kinematic age, assuming that pulsars are born near the Galactic plane. We derive kinematic ages for 52 pulsars, based on the measured pulsar proper motions and positions, by modelling the trajectory of the pulsars in a Galactic potential. The sample of 52 pulsar kinematic ages constitutes the largest number of independently estimated pulsar ages to date. Using only the 33 most reliable kinematic ages from our simulations, we revisit the evolution of spin- velocity alignment, this time as a function of kinematic age. We find that the strong correlation seen in young pulsars is completely smeared out for pulsars with kinematic ages above 10 Myr, a length of time beyond which we expect the gravitational pull of the Galaxy to have a significant effect on the directions of pulsar velocities. In the discussion, we investigate the impact of large distance uncertainties on the reliability of the calculated kinematic ages. Furthermore, we present a detailed investigation of the implications of our revised pulsar ages for the braking-index and birth-period distributions. Finally, we discuss the predictions of various SN-kick mechanisms and their compatibility with our results.