Radiation from Axion star-Neutron star binaries with a tilted rotation axis in the presence of plasma

TL;DR

This paper studies the electromagnetic radiation emitted by axion star-neutron star binaries, highlighting how the neutron star's tilted spin enhances radiation and examining plasma effects on emission.

Contribution

It introduces a model with a sech profile for axion stars and analyzes the impact of neutron star spin tilt and plasma on emitted radiation.

Findings

Tilted neutron star spin significantly increases radiated power.

Dilute axion stars can radiate more efficiently than dense ones.

Tidal forces can disrupt dilute axion stars before significant radiation occurs.

Abstract

We investigate the form of the radiation emitted by an axion star-neutron star binary using a $f(r)=\text{sech(r/R)}$ profile for the axion star. Our analysis takes into account the co-rotating plasma of the neutron star. We find that that there is significant enhancement to the radiated power if the neutron star's spin is tilted towards the plane of the axion star-neutron star orbit, compared to the case where it is perpendicular. We also examine whether the neutron star's co-rotating plasma can play a role in the emitted power and we find that even though dilute axion stars can in principle radiate more efficiently than dense axion stars, they will be pulled apart by the tidal forces of the neutron star