All-sky coherent search for continuous gravitational waves in 6-7 Hz band with a torsion-bar antenna

TL;DR

This paper reports on an all-sky search for continuous gravitational waves in the 6-7 Hz band using an upgraded torsion-bar antenna (TOBA), setting upper limits on GW strain but detecting no signals.

Contribution

The study demonstrates the first all-sky coherent search in the 6-7 Hz band with a TOBA, providing new upper limits on continuous gravitational waves in this low-frequency range.

Findings

No significant GW signals detected in 6-7 Hz band.

Established the most stringent upper limit on GW strain at 6.84 Hz.

Achieved strain sensitivity of 10^{-10} Hz^{-1/2} at 1 Hz.

Abstract

A torsion-bar antenna (TOBA) is a low-frequency terrestrial gravitational wave (GW) antenna which consists of two orthogonal bar-shaped test masses. We upgraded the prototype TOBA and achieved the strain sensitivity $10^{-10}$ Hz$^{-1/2}$ at around 1 Hz. We operated the upgraded TOBA (called the "Phase-II TOBA") located at Tokyo in Japan for 22.5 hours and performed an all-sky coherent search for continuous GWs using the $\mathcal{F}$-statistic. We place upper limits on continuous GWs from electromagnetically unknown sources in the frequency range from 6 Hz to 7 Hz with the first derivative of frequency less than $7.62 \times 10^{-11}$ Hz/s using data from the TOBA. As a result, no significant GW signals are found in the frequency band 6-7 Hz. The most stringent upper limit upper limit on the dimensionless GW strain with 95% confidence level in this band is $3.6 \times 10^{-12}$ at 6.84 Hz.