A Population of Non-Recycled Pulsars Orginating in Globular Clusters

TL;DR

This paper investigates the origin and detectability of non-recycled pulsars in globular clusters, focusing on their birth kicks and potential to be distinguished from disk pulsars in future surveys.

Contribution

It models the kick velocities of pulsars from electron capture supernovae and assesses the likelihood of identifying cluster-origin pulsars in large-scale surveys.

Findings

Realistic kick velocities are less than ~10 km/s.

The pulsar population correlates with cluster luminosity.

Detection prospects are limited, with less than 10% detectable by future surveys.

Abstract

We explore the enigmatic population of long-period, apparently non-recycled pulsars in globular clusters, building on recent work by Boyles et al (2011). This population is difficult to explain if it formed through typical core collapse supernovae, leading many authors to invoke electron capture supernovae. Where Boyles et al. dealt only with non-recycled pulsars in clusters, we focus on the pulsars that originated in clusters but then escaped into the field of the Galaxy due to the kicks they receive at birth. The magnitude of the kick induced by electron capture supernovae is not well known, so we explore various models for the kick velocity distribution and size of the population. The most realistic models are those where the kick velocity is <~ 10 km/s and where the number of pulsars scales with the luminosity of the cluster (as a proxy for cluster mass). This is in good agreement with other estimates of the electron capture supernovae kick velocity. We simulate a number of large-area pulsar surveys to determine if a population of pulsars originating in clusters could be identified as being separate from normal disk pulsars. We find that the spatial and kinematical properties of the population could be used, but only if large numbers of pulsars are detected. In fact, even the most optimistic surveys carried out with the future Square Kilometer Array are likely to detect < 10% of the total population, so the prospects for identifying these as a separate group of pulsars are presently poor.