# SOAP: A generalised application of the Viterbi algorithm to searches for continuous gravitational-wave signals

## TL;DR

This paper introduces a Viterbi algorithm-based search method for continuous gravitational waves that is model-agnostic, computationally efficient, and capable of detecting signals with unknown frequency evolution, demonstrated on real and simulated data.

## Contribution

The authors develop a novel, computationally efficient Viterbi-based search method for continuous gravitational waves that is less sensitive but more versatile than traditional template-matching approaches.

## Key findings

- Achieves 95% efficiency with 1% false alarm rate in various datasets.
- Depth sensitivities of approximately 33, 10, and 13 Hz^{-1/2} in different data sets.
- SNRs of about 60, 72, and 74 in the tested datasets.

## Abstract

All-sky and wide parameter space searches for continuous gravitational waves are generally template-matching schemes which test a bank of signal waveforms against data from a gravitational wave detector. Such searches can offer optimal sensitivity for a given computing cost and signal model, but are highly-tuned to specific signal types and are computationally expensive, even for semi-coherent searches. We have developed a search method based on the well-known Viterbi algorithm which is model-agnostic and has a computational cost several orders of magnitude lower than template methods, with a modest reduction in sensitivity. In particular, this method can search for signals which have an unknown frequency evolution. We test the algorithm on three simulated and real data sets: gapless Gaussian noise, Gaussian noise with gaps and real data from the final run of initial LIGO (S6). We show that at 95% efficiency, with a 1% false alarm rate, the algorithm has a depth sensitivity of $\sim 33$, $10$ and $13$ ,Hz$^{-1/2}$ with corresponding SNRs of $\sim 60$, $72$ and $74$ in these datasets. we discuss the use of this algorithm for detecting a wide range of quasi-monochromatic gravitational wave signals and instrumental lines.