Searching for stochastic gravitational waves using co-located interferometric detectors

Abstract

Despite their intrinsic advantages due to co-location, the two LIGO (Laser Interferometer Gravitational Wave Observatory) 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 thesis, using data from LIGO's fourth science run, 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. Next, using this frequency veto technique and data from the first epoch of LIGO's fifth, currently running science run, we design, implement, and perform a search for astrophysical populations of gravitational wave emitters, which emit predominantly in the kilohertz region of the spectrum, a region totally inaccessible to detectors separated by thousands of kilometers. As well as providing us with a proof-of-concept, the results provide an advanced look at the physical results to come from H1-H2 by the end of S5.