Ground-based low-frequency gravitational-wave detector with multiple outputs

Abstract

We have developed a new gravitational-wave (GW) detector, TOrsion-Bar Antenna (TOBA), which has a multiple-output configuration. TOBA is a detector with bar-shaped test masses that are rotated by the tidal force of the GWs. In our detector, three independent signals can be derived from the GW by monitoring multiple rotational degrees of freedom, i.e., the horizontal rotations and vertical rotations of the bars. Since the three outputs have different antenna pattern functions, the multioutput system improves the detection rate and the parameter estimation accuracy. This is useful for obtaining further details about the GW sources, such as population and directions. We successfully operated the multioutput detector continuously for more than 24 hours with stable data quality. The GW equivalent strain noise in one of the signals has been reduced to $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{ }{\mathrm{Hz}}^{\ensuremath{-}1/2}$ at 3 Hz by a combination of passive and active vibration isolation systems, while the sensitivities to possible GW signals derived from the vertical rotations are worse than that from the horizontal rotation.