Search for continuous gravitational waves from Fomalhaut b in the second Advanced LIGO observing run with a hidden Markov model

TL;DR

This study conducted a semicoherent search for continuous gravitational waves from Fomalhaut b using Advanced LIGO data and a hidden Markov model, setting upper limits but finding no definitive signals.

Contribution

Introduces a novel semicoherent search method combining a hidden Markov model with an $ ext{F}$-statistic for detecting continuous gravitational waves.

Findings

No strong evidence of continuous waves was detected.

Established upper limits on gravitational wave strain at 90% confidence.

Identified one candidate for further analysis, but not confirmed.

Abstract

Results are presented from a semicoherent search for continuous gravitational waves from a nearby neutron star candidate, Fomalhaut b, using data collected in the second observing run of Advanced LIGO. The search is based on a hidden Markov model scheme, capable of tracking signal frequency evolution from the star's secular spin down and stochastic timing noise simultaneously. The scheme is combined with a frequency domain matched filter ($\mathcal{F}$-statistic), calculated coherently over five-day time stretches. The frequency band 100-1000 Hz is searched. After passing the above-threshold candidates through a hierarchy of vetoes, one candidate slightly above the 1% false alarm probability threshold remains for further scrutiny. No strong evidence of continuous waves is found. We present the strain upper limits in the full frequency band searched at 90% confidence level.