Constraints on Weak Supernova Kicks from Observed Pulsar Velocities

TL;DR

This paper investigates the distribution of pulsar velocities to understand the strength of natal kicks received at birth, proposing a binary interaction-dependent model that aligns with observations without reducing neutron star merger predictions.

Contribution

It introduces a model linking low natal kicks to binary interactions, explaining observed pulsar velocities and preserving neutron star merger rates.

Findings

Low natal kicks are associated with electron-capture supernovae in binary systems.

The model reproduces observed pulsar velocity distributions.

The progenitor mass range for electron-capture supernovae is narrowly constrained.

Abstract

Observations of binary pulsars and pulsars in globular clusters suggest that at least some pulsars must receive weak natal kicks at birth. If all pulsars received strong natal kicks above \unit[50]{\kms}, those born in globular clusters would predominantly escape, while wide binaries would be disrupted. On the other hand, observations of transverse velocities of isolated radio pulsars indicate that only $5\pm2\%$ have velocities below \unit[50]{\kms}. We explore this apparent tension with rapid binary population synthesis modelling. We propose a model in which supernovae with characteristically low natal kicks (e.g., electron-capture supernovae) only occur if the progenitor star has been stripped via binary interaction with a companion. We show that this model naturally reproduces the observed pulsar speed distribution and without reducing the predicted merging double neutron star yield. We estimate that the zero-age main sequence mass range for non-interacting progenitors of electron-capture supernovae should be no wider than ${\approx}0.2 M_\odot$.