Evolving neutron star+helium star systems to intermediate-mass binary pulsars

TL;DR

This study investigates the evolution of neutron star+helium star systems into intermediate-mass binary pulsars, demonstrating that certain accretion models can explain most observed systems, including well-measured cases like PSR J0621+1002.

Contribution

It introduces a detailed modeling of NS+He star evolution with variable accretion rates and NS masses, successfully reproducing observed IMBP properties, especially for short orbital periods.

Findings

Most observed IMBPs with short orbital periods are explained.

The accretion rate proportional to M_NS^(-1/3) fits observations well.

Final NS spin periods slightly decrease with initial NS mass.

Abstract

Intermediate-mass binary pulsars (IMBPs) are composed of neutron stars (NSs) and CO/ONe white dwarfs (WDs). It is generally suggested that IMBPs evolve from intermediate-mass X-ray binaries (IMXBs). However, this scenario is difficult to explain the formation of IMBPs with orbital periods ($P_{\rm orb}$) less than 3 d. It has recently been proposed that a system consisting of a neutron star (NS) and a helium (He) star can form IMBPs with $P_{\rm orb}$ less than 3 d (known as the NS+He star scenario), but previous works can only cover a few observed sources with short orbital periods. We aim to investigate the NS+He star scenario by adopting different descriptions of the Eddington accretion rate ($\dot M_{\rm Edd}$) for NSs and different NS masses ($M_{\rm NS}$) varying from $1.10\,\rm M_{\odot}$ to $1.80\,\rm M_{\odot}$. Our results can cover most of the observed IMBPs with short orbital periods and almost half of the observed IMBPs with long orbital periods. We found that $\dot{M}_{\rm Edd}$$\propto$$M_{\rm NS}$$^{\rm -1/3}$ could match the observations better than a specific value for all NSs. We also found that the final spin periods of NSs slightly decrease with the initial $M_{\rm NS}$. The observed parameters of PSR J0621+1002, which is one of the well-observed IMBPs whose pulsar mass has been precisely measured, can be reproduced by the present work.