Identifying correlated environmental noise in co-located interferometers with application to stochastic gravitational wave analysis

Abstract

Despite their intrinsic advantages due to co-location, the two LIGO Hanford interferometers have not been used in the search for the stochastic gravitational wave background due to their coupling to a shared environment, which may be comparable to or exceed any gravitational signal. In this paper, using S4 data, we demonstrate a technique to relate the H1–H2 coherence to coupling with physical environmental channels. We show that the correspondence is tight enough to correctly identify regions of high and low coupling and the nature of the coupling in the data set. A simple thresholding provides frequency vetoes, which we can use to derive a significantly cleaner coherence spectrum. The output of this preliminary investigation suggests that H1–H2 may soon be ready to contribute to the stochastic search.