Parameter-space metric of semicoherent searches for continuous gravitational waves

TL;DR

This paper develops an analytical parameter-space metric for semicoherent searches of continuous gravitational waves, improving understanding of the search parameter structure and enhancing the efficiency of hierarchical detection strategies.

Contribution

It introduces the first analytical parameter-space metric for the incoherent combination step in semicoherent CW searches, applicable to broadband all-sky surveys.

Findings

The metric resolution in frequency derivatives increases with the number of segments.

New coordinates on parameter space facilitate analytical metric derivation.

The metric applies to both all-sky and directed CW searches.

Abstract

Continuous gravitational-wave (CW) signals such as emitted by spinning neutron stars are an important target class for current detectors. However, the enormous computational demand prohibits fully coherent broadband all-sky searches for prior unknown CW sources over wide ranges of parameter space and for yearlong observation times. More efficient hierarchical "semicoherent" search strategies divide the data into segments much shorter than one year, which are analyzed coherently; then detection statistics from different segments are combined incoherently. To optimally perform the incoherent combination, understanding of the underlying parameter-space structure is requisite. This problem is addressed here by using new coordinates on the parameter space, which yield the first analytical parameter-space metric for the incoherent combination step. This semicoherent metric applies to broadband all-sky surveys (also embedding directed searches at fixed sky position) for isolated CW sources. Furthermore, the additional metric resolution attained through the combination of segments is studied. From the search parameters (sky position, frequency, and frequency derivatives), solely the metric resolution in the frequency derivatives is found to significantly increase with the number of segments.