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

Abstract

Recently, a braking index for the pulsar PSR J1640-4631 has been measured. With a braking index of n = 3.15 ± 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 (GW) brake yields n = 5. Therefore, each of these mechanisms alone can not account for the braking index found for PSR J1640-4631. Here we consider in detail that such a braking index could be accounted for if the spindown model combines magnetic dipole and GW 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 GW that comes from our model is around a factor four lower than the amplitude modeled exclusively by GW energy loss. Another interesting outcome of our modeling is that it is possible to obtain the ellipticity from the braking index and other pulsar parameters.