Probing the propeller regime with wide neutron star binaries

TL;DR

This paper models the propeller stage duration in wide neutron star binaries, exploring conditions for accretion onset and the impact of magnetic fields and spin-down rates, with implications for systems like SWIFT J0850.8-4219.

Contribution

It introduces a detailed modeling approach for the propeller phase duration and accretion conditions in wide neutron star binaries, considering different propeller spin-down scenarios.

Findings

Accretion is unlikely in systems like SWIFT J0850.8-4219 unless slow spin-down occurs.

Neutron stars with magnetic fields below 10^{12} G at separations over 1 AU do not reach the propeller stage.

Fast propeller spin-down prevents neutron stars from ever accreting.

Abstract

We model the duration of the propeller stage in wide binary systems with neutron stars and calculate the time of accretion onset for various propeller models. We apply our modeling to the symbiotic X-ray binary SWIFT J0850.8-4219. Unless a propeller with a very slow spin-down is operating, it is very improbable to find a system similar to SWIFT J0850.8-4219 at the propeller stage. Then we model the evolution of a neutron star in a binary with a solar-like companion. We calculate for which orbital separations and magnetic fields a neutron star can start to accrete while the companion is still on the Main sequence. We demonstrate that for the magnetic field $B\lesssim10^{12}$~G neutron stars at the orbital separation $a\gtrsim 1$~AU do not reach the propeller stage. In the case of a slow propeller spin-down, neutron stars never start to accrete. For the more rapid propeller spin-down, a neutron star can start to accrete or spend a long time at the propeller stage depending on the parameters.