How rapidly do neutron stars spin at birth?

TL;DR

This study investigates the X-ray emissions of aging supernova remnants to infer the birth spin periods of neutron stars, finding that most are unlikely to have been born spinning faster than approximately 40 milliseconds.

Contribution

The paper provides observational constraints on the initial spin periods of neutron stars by analyzing X-ray data and comparing it with Monte Carlo simulations.

Findings

No luminous young pulsars observed above ~10^{37} erg/s.

Population with birth periods <~ 40 ms is inconsistent with data.

Constraints suggest slower initial neutron star spins.

Abstract

We have studied the X-ray properties of ageing historical core-collapse supernovae in nearby galaxies, using archival data from Chandra, XMM-Newton and Swift. We found possible evidence of a young X-ray pulsar in SN 1968D and in few other sources, but none more luminous than ~ a few 10^{37} erg/s. We compared the observational limits to the X-ray pulsar luminosity distribution with the results of Monte Carlo simulations for a range of birth parameters. We conclude that a pulsar population dominated by periods <~ 40 ms at birth is ruled out by the data.