Gravitational wave emission by the high braking index pulsar PSR J1640-4631

TL;DR

This paper models the high braking index of pulsar PSR J1640-4631 as a combination of magnetic dipole and gravitational wave braking, providing insights into its gravitational wave emission and ellipticity.

Contribution

It introduces a combined braking model explaining the pulsar's high braking index and estimates its gravitational wave amplitude and ellipticity.

Findings

Braking index can be explained by combined magnetic and gravitational wave braking.

Gravitational wave amplitude is about four times lower than pure gravitational wave models.

Ellipticity of the pulsar can be derived from the braking index and pulsar parameters.

Abstract

Recently, a braking index for the pulsar PSR J1640-4631 has been measured. With a braking index of $n = 3.15 \pm 0.03$, this pulsar has the highest braking index ever measured. As it is well known, a pure magnetic dipole brake yields $n = 3$, whereas a pure gravitational wave brake yields $n = 5$. Therefore, each of these mechanisms alone can not account for the braking index found for PSR J1640-4631. Here we show that such a braking index can be accounted for if the spindown model combines magnetic dipole and gravitational wave brakes. Then, we briefly discuss the detectability of this pulsar by aLIGO and the planned Einstein Telescope. In particular, we show that the amplitude of the gravitational wave that comes from our model is around a factor four lower than the amplitude modeled exclusively by gravitational wave energy loss. Another interesting outcome of our modeling is that we are able to obtain the ellipticity from the braking index and other pulsar parameters.