Measurement and subtraction of Schumann resonances at gravitational-wave interferometers

Abstract

Correlated magnetic noise from Schumann resonances threatens to contaminate the observation of a stochastic gravitational-wave background in interferometric detectors. In previous work, we reported on the first effort to eliminate global correlated noise from the Schumann resonances using Wiener filtering, demonstrating as much as a factor of two reduction in the coherence between magnetometers on different continents. In this work, we present results from dedicated magnetometer measurements at the Virgo and KAGRA sites, which are the first results for subtraction using data from gravitational-wave detector sites. We compare these measurements to a growing network of permanent magnetometer stations, including at the LIGO sites. We show the effect of mutual magnetometer attraction, arguing that magnetometers should be placed at least one meter from one another. In addition, for the first time, we show how dedicated measurements by magnetometers near to the interferometers can reduce coherence to a level consistent with uncorrelated noise, making a potential detection of a stochastic gravitational-wave background possible.

Investigation of magnetic noise in advanced Virgo

“…For this reason a LIGO-Virgo joint experimental evaluation of the global MN contribution may be worth investigating in the future. In anticipation of that, it has been decided to keep monitoring the global MN activity at each GW site with dedicated low-noise magnetometers [9]. Similarly it has been proposed to perform MN injections on a weekly/monthly basis, during the normal scientific run, to keep track of the magnetic transfer function.…”

Search for the isotropic stochastic background using data from Advanced LIGO’s second observing run

“…Coherent noise between gravitational-wave interferometers may be introduced by terrestrial sources such as Schumann resonances, which are global electromagnetic modes of the cavity formed by the Earth's surface and ionosphere [71]. These fields have very long coherence lengths [110] and can magnetically couple to the gravitational-wave channel and lead to broadband noise that is coherent between different gravitational-wave detectors. As the detectors become more sensitive, eventually this source of correlated noise may become visible to the crosscorrelation search and, if not treated carefully, will bias the analysis by appearing as an apparent stochastic background.…”

“…4. Additionally, work is ongoing to develop Wiener filtering to subtract Schumann noise [110,112,115] and to develop a parameter estimation framework to measure or place upper limits on the level of magnetic contamination [116]. This work will take advantage of low noise LEMI-120 magnetometers [117] that were recently installed at both LIGO sites, as described in the Supplemental Material [87].…”

Correlated magnetic noise from anisotropic lightning sources and the detection of stochastic gravitational waves

“…[22][23][24]. While the recent study suggests that the correlated noise budget including the one arising from the Schumann resonance is less significant and ignorable at LIGO detectors [25], the potential impact still remains at other detector sites, and a clear signal of Schumann resonances has been indeed detected through the magnetometer measurements between Virgo [26] and KAGRA [27] sites [28].…”