Correlated Magnetic Noise in the Advanced LIGO Detector

A stochastic gravitational wave background is expected to arise as the result of many overlapping, individually indistinguishable sources. Such a background is measured by correlating the strain signal in two detectors like those part of the Laser Interferometer Gravitational Wave Observatory (LIGO). The two detectors must be sufficiently far apart to minimize common noise sources, which create correlated noise that doesn’t decrease with increased integration time. One possible source of correlated noise is Schumann resonances–global magnetic fields produced by lightning strikes that excite the Earth-Ionosphere cavity. After a series of updates designed to improve detector sensitivity, the Advanced LIGO (aLIGO) instrument will begin its first science run in the Fall of 2015. In this paper, we analyze the magnetic contribution to correlated noise and present an updated noise budget for the data from the latest engineering run in preparation for aLIGO’s first science run.