Coherently combining short data segments for all-sky semi-coherent continuous gravitational wave searches

TL;DR

This paper introduces a method to coherently combine short data segments in all-sky semi-coherent gravitational wave searches, enhancing sensitivity while addressing computational and parameter uncertainty challenges.

Contribution

It presents a novel technique using summed Fourier coefficients to improve semi-coherent search sensitivity for continuous gravitational waves.

Findings

Coherent combination improves search sensitivity.

Method works with the TwoSpect algorithm.

Careful parameter marginalization is necessary for misaligned detectors.

Abstract

We present a method for coherently combining short data segments from gravitational-wave detectors to improve the sensitivity of semi-coherent searches for continuous gravitational waves. All-sky searches for continuous gravitational waves from unknown sources are computationally limited. The semi-coherent approach reduces the computational cost by dividing the entire observation timespan into short segments to be analyzed coherently, then combined together incoherently. Semi-coherent analyses that attempt to improve sensitivity by coherently combining data from multiple detectors face a computational challenge in accounting for uncertainties in signal parameters. In this article, we lay out a technique to meet this challenge using summed Fourier transform coefficients. Applying this technique to one all-sky search algorithm called TwoSpect, we confirm that the sensitivity of all-sky, semi-coherent searches can be improved by coherently combining the short data segments. For misaligned detectors, however, this improvement requires careful attention when marginalizing over unknown polarization parameters. In addition, care must be taken in correcting for differential detector velocity due to the Earth's rotation for high signal frequencies and widely separated detectors.