We present the first upper limit on gravitational wave (GW) backgrounds at an unexplored frequency of 0.2 Hz using a torsion-bar antenna (TOBA). A TOBA was proposed to search for low-frequency GWs. We have developed a small-scaled TOBA and successfully found {\Omega}gw(f) < 4.3 \times 1017 at 0.2 Hz as demonstration of the TOBA's capabilities, where {\Omega}gw (f) is the GW energy density per logarithmic frequency interval in units of the closure density. Our result is the first nonintegrated limit to bridge the gap between the LIGO band (around 100 Hz) and the Cassini band (10-6 - 10-4 Hz).
@article{arxiv.1103.0346,
title = {Upper Limit on Gravitational Wave Backgrounds at 0.2 Hz with Torsion-bar Antenna},
author = {Koji Ishidoshiro and Masaki Ando and Akiteru Takamori and Hirotaka Takahashi and Kenshi Okada and Nobuyuki Matsumoto and Wataru Kokuyama and Nobuyuki Kanda and Yoichi Aso and Kimio Tsubono},
journal= {arXiv preprint arXiv:1103.0346},
year = {2011}
}