Correlated noise in networks of gravitational-wave detectors: subtraction and mitigation

TL;DR

This paper assesses the impact of correlated magnetic noise on gravitational-wave detectors, explores subtraction methods, and estimates how residual noise could limit stochastic background measurements.

Contribution

It introduces a formalism for subtracting correlated noise in gravitational-wave data and evaluates its effectiveness for improving stochastic background searches.

Findings

Correlated magnetic noise can significantly affect LIGO's measurements.

Wiener filtering could reduce correlated noise but may not eliminate it entirely.

Residual noise could increase uncertainty in energy density estimates by up to a factor of 4.

Abstract

One of the key science goals of advanced gravitational-wave detectors is to observe a stochastic gravitational-wave background. However, recent work demonstrates that correlated magnetic fields from Schumann resonances can produce correlated strain noise over global distances, potentially limiting the sensitivity of stochastic background searches with advanced detectors. In this paper, we estimate the correlated noise budget for the worldwide Advanced LIGO network and conclude that correlated noise may affect upcoming measurements. We investigate the possibility of a Wiener filtering scheme to subtract correlated noise from Advanced LIGO searches, and estimate the required specifications. We also consider the possibility that residual correlated noise remains following subtraction, and we devise an optimal strategy for measuring astronomical parameters in the presence of correlated noise. Using this new formalism, we estimate the loss of sensitivity for a broadband, isotropic stochastic background search using 1 yr of LIGO data at design sensitivity. Given our current noise budget, the uncertainty with which LIGO can estimate energy density will likely increase by a factor of ~4--if it is impossible to achieve significant subtraction. Additionally, narrowband cross-correlation searches may be severely affected at low frequencies f < 45 Hz without effective subtraction.