Gravitational waves from post-merger radially-oscillating millisecond pulsars

TL;DR

This paper explores how rotation-induced gravitational waves from radially oscillating, rapidly rotating pulsars formed after neutron star mergers could be detectable, providing insights into post-merger dynamics and neutron star physics.

Contribution

It introduces a mechanism for gravitational wave emission from radially oscillating pulsars post-merger and estimates its detectability with current and future detectors.

Findings

Radial oscillations can be efficiently damped by gravitational radiation.

The gravitational wave contribution to high-frequency spectrum is significant.

Event rates suggest potential detectability with advanced detectors.

Abstract

Observations of short-duration gamma-ray bursts and their afterglows show that a good fraction (perhaps $\gtrsim50\%$) of binary neutron star mergers lead to strongly magnetized, rapidly rotating pulsars (including millisecond magnetars), no matter whether the pulsar remnants are short- or long-lived. Such compact objects are very likely to have significant radial oscillations and high interior temperatures, as indicated in recent numerical simulations. In this paper, we have investigated rotation-induced gravitational radiation from possibly existing, radially oscillating pulsars after binary neutron star mergers, and find that this mechanism can efficiently damp the radial oscillations. The resulting gravitational waves (GWs) could have a non-negligible contribution to the high-frequency spectrum. We provide an order-of-magnitude estimate of the event rate and suggest that such GW events would be detectable with the advanced LIGO/Virgo or next-generation detectors. Our discussion can also be applied to newborn, radially oscillating, millisecond pulsars formed through the other astrophysical processes.