Combined analysis of neutron star natal kicks using proper motions and parallax measurements for radio pulsars and Be X-ray binaries

TL;DR

This study constrains neutron star natal kicks by combining proper motion and parallax data from radio pulsars and Be X-ray binaries, proposing a new kick model consistent with observations.

Contribution

It introduces a robust statistical method to analyze diverse observational data and proposes a new model for neutron star natal kicks compatible with multiple measurements.

Findings

Best-fit natal kick model includes a mix of weak and high-velocity kicks.

Current electron capture supernova kick models are inconsistent with observations.

A new ecSN kick model aligns with data from both pulsars and X-ray binaries.

Abstract

Supernova explosion and the associated neutron star natal kicks are important events on a pathway of a binary to become a gravitational wave source, an X-ray binary or a millisecond radio pulsar. Weak natal kicks often lead to binary survival, while strong kicks frequently disrupt the binary. In this article, we aim to further constrain neutron star natal kicks in binaries. We explore binary population synthesis models by varying prescription for natal kick, remnant mass and mass accretion efficiency. We introduce a robust statistical technique to analyse combined observations of different nature. Using this technique, we further test different models using parallax and proper motion measurements for young isolated radio pulsars and similar measurements for Galactic Be X-ray binaries. Our best model for natal kicks is consistent with both measurements and contains a fraction of $w=0.2\pm 0.1$ weak natal kicks with $\sigma_1 = 45^{+25}_{-15}$ km/s, the remaining natal kicks are drawn from the high-velocity component, same as in previous works: $\sigma_2 = 336$ km/s. We found that currently used models for natal kicks of neutron stars produced by electron capture supernova (combination of maxwellian $\sigma=265$ km/s and $\sigma = 30$ km/s for electron capture) are inconsistent or marginally consistent with parallaxes and proper motions measured for isolated radio pulsars. We suggest a new model for natal kicks of ecSN, which satisfy both observations of isolated radio pulsars and Be X-ray binaries.