The effect of kick velocities on the spatial distribution of millisecond pulsars and implications for the Galactic center excess

TL;DR

This study uses N-body simulations and gamma-ray MSP proper motions to analyze how natal kick velocities influence the spatial distribution of millisecond pulsars, impacting their role in explaining the Galactic center excess.

Contribution

It models the effect of natal kicks on MSP distribution using simulations and gamma-ray data, providing new insights into their spatial spread in the Galactic bulge.

Findings

Natal kicks cause ~10% increase in MSP distribution dimensions.

MSP distribution becomes less boxy due to kicks.

Distribution remains far from spherical despite kicks.

Abstract

Recently it has become apparent that the Galactic center excess (GCE) is spatially correlated with the stellar distribution in the Galactic bulge. This has given extra motivation for the unresolved population of millisecond pulsars (MSPs) explanation for the GCE. However, in the "recycling" channel the neutron star forms from a core collapse supernovae that undergoes a random "kick" due to the asymmetry of the explosion. This would imply a smoothing out of the spatial distribution of the MSPs. We use N-body simulations to model how the MSP spatial distribution changes. We estimate the probability distribution of natal kick velocities using the resolved gamma-ray MSP proper motions, where MSPs have random velocities relative to the circular motion with a scale parameter of 77+/-6 km/s. We find that, due to the natal kicks, there is an approximately 10% increase in each of the bulge MSP spatial distribution dimensions and also the bulge MSP distribution becomes less boxy but is still far from being spherical.