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

Abstract

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 (Porb) less than 3 d. It has recently been proposed that a system consisting of an NS and a helium (He) star can form IMBPs with Porb 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 ($\skew4\dot{M}_{\rm Edd}$) for NSs and different NS masses (MNS) varying from $1.10$ 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 $\skew4\dot{M}_{\rm Edd}$ ∝ MNS−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 MNS. 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 this work.