Designing a cross-correlation search for continuous-wave gravitational radiation from a neutron star in the supernova remnant SNR 1987A

TL;DR

This paper presents a new semi-coherent cross-correlation search strategy for detecting gravitational waves from a young neutron star in SNR 1987A, incorporating an astrophysical model that accounts for spin-down via magnetic field and ellipticity.

Contribution

It introduces a novel astrophysical phase model for gravitational wave searches that accurately tracks neutron star spin-down with constant braking index, improving detection prospects.

Findings

Theoretical sensitivity exceeds age-based upper limits in 75-450 Hz band.

Estimated search parameter space covers ~10^9 templates.

Potential to set new limits on magnetic field and ellipticity if no detection occurs.

Abstract

A strategy is devised for a semi-coherent cross-correlation search for a young neutron star in the supernova remnant SNR 1987A, using science data from the Initial LIGO and/or Virgo detectors. An astrophysical model for the gravitational wave phase is introduced which describes the star's spin down in terms of its magnetic field strength $B$ and ellipticity $\epsilon$, instead of its frequency derivatives. The model accurately tracks the gravitational wave phase from a rapidly decelerating neutron star under the restrictive but computationally unavoidable assumption of constant braking index, an issue which has hindered previous searches for such young objects. The theoretical sensitivity is calculated and compared to the indirect, age-based wave strain upper limit. The age-based limit lies above the detection threshold in the frequency band 75\,Hz $\lesssim \nu \lesssim 450$\,Hz. The semi-coherent phase metric is also calculated and used to estimate the optimal search template spacing for the search. The range of search parameters that can be covered given our computational resources ($\sim 10^9$ templates) is also estimated. For Initial LIGO sensitivity, in the frequency band between 50\,Hz and 500\,Hz, in the absence of a detected signal, we should be able to set limits of $B \gtrsim 10^{11}$\,G and $\epsilon \lesssim 10^{-4}$.