Analysis of First LIGO Science Data for Stochastic Gravitational Waves

TL;DR

This paper analyzes initial LIGO data to set upper limits on the stochastic gravitational wave background, demonstrating significant improvements over previous limits and outlining methods for future sensitivity enhancements.

Contribution

It introduces detailed data analysis techniques for real interferometric data and establishes the first upper limit on a stochastic gravitational wave background from LIGO's first science run.

Findings

Established an upper limit of Omega_0 h_{100}^2 < 23 at 90% confidence

Achieved a limit approximately 10^4 times better than previous broadband limits

Demonstrated analysis procedures for future sensitivity improvements

Abstract

We present the analysis of between 50 and 100 hrs of coincident interferometric strain data used to search for and establish an upper limit on a stochastic background of gravitational radiation. These data come from the first LIGO science run, during which all three LIGO interferometers were operated over a 2-week period spanning August and September of 2002. The method of cross-correlating the outputs of two interferometers is used for analysis. We describe in detail practical signal processing issues that arise when working with real data, and we establish an observational upper limit on a f^{-3} power spectrum of gravitational waves. Our 90% confidence limit is Omega_0 h_{100}^2 < 23 in the frequency band 40 to 314 Hz, where h_{100} is the Hubble constant in units of 100 km/sec/Mpc and Omega_0 is the gravitational wave energy density per logarithmic frequency interval in units of the closure density. This limit is approximately 10^4 times better than the previous, broadband direct limit using interferometric detectors, and nearly 3 times better than the best narrow-band bar detector limit. As LIGO and other worldwide detectors improve in sensitivity and attain their design goals, the analysis procedures described here should lead to stochastic background sensitivity levels of astrophysical interest.