Evolution of Transient Low-Mass X-ray Binaries to Redback Millisecond Pulsars

TL;DR

This paper proposes that the evolution of transient low-mass X-ray binaries, through disk instability and quiescence phases, can lead to the formation of redback millisecond pulsars, highlighting an evolutionary link between these systems.

Contribution

It introduces a binary evolution model showing how disk instability and quiescence in LMXBs can produce redback pulsars, suggesting a new formation pathway.

Findings

Disk instability covers the redback parameter space.

Quiescence reduces accretion, activating pulsar emission.

Evaporation feedback influences redback evolution.

Abstract

Redback millisecond pulsars (hereafter redbacks) are a sub-population of eclipsing millisecond pulsars in close binaries. The formation processes of these systems are not clear. The three pulsars showing transitions between rotation- and accretion-powered states belong to both redbacks and transient low-mass X-ray binaries (LMXBs), suggesting a possible evolutionary link between the them. Through binary evolution calculations, we show that the accretion disks in almost all LMXBs are subject to the thermal-viscous instability during certain evolutionary stages, and the parameter space for the disk instability covers the distribution of known redbacks in the orbital period - companion mass plane. We accordingly suggest that the abrupt reduction of the mass accretion rate during quiescence of transient LMXBs provides a plausible way to switch on the pulsar activity, leading to the formation of redbacks, if the neutron star has been spun up to be an energetic millisecond pulsar. We investigate the evolution of redbacks, taking into account the evaporation feedback, and discuss its possible influence on the formation of black widow millisecond pulsars.