What Makes an Accretion-Powered Millisecond Pulsar?

TL;DR

This paper explores how neutron star mass influences the detectability of accretion-powered millisecond pulsars, suggesting that lower mass and transient accretion increase pulsation detection likelihood.

Contribution

It introduces a mechanism linking neutron star mass and accretion behavior to pulsar detection rates, explaining the scarcity of observed millisecond pulsars.

Findings

Pulsation amplitudes decrease with increasing neutron star mass.

Transient, low-Mdot systems are more likely to show detectable pulsations.

The mechanism accounts for the low number of observed millisecond pulsars.

Abstract

We investigate the dependence of pulse amplitudes of accreting millisecond pulsars on the masses of the neutron stars. Because the pulsation amplitudes are suppressed as the neutron stars become more massive, the probability of detection of pulsations decreases in systems that have been accreting for a long time. However, the probability of detectable pulsations is higher in transient systems where the mass accretion is sporadic and the neutron star is likely to have a low mass. We propose this mechanism as the explanation of the small number of millisecond X-ray pulsars found to date, as well as their emergence as fast pulsars mostly in transient, low-Mdot systems. This mechanism can also quantitatively explain the lack of pulsars in the majority of LMXBs.