Initial Results from the LIGO Newtonian Calibrator

Abstract

The precise calibration of the strain readout of the LIGO gravitational wave observatories is paramount to the accurate interpretation of gravitational wave events. This calibration is traditionally done by imparting a known force on the test masses of the observatory via radiation pressure.Here we describe the implementation of an alternative calibration scheme: the Newtonian Calibrator. This system uses a rotor consisting of both quadrupole and hexapole mass distributions to apply a time-varying gravitational force on one of the observatory's test masses. The force produced by this rotor can be predicted to < 1% relative uncertainty and is well-resolved in the readout of the observatory. This system currently acts as a cross-check of the existing absolute calibration system.

Calibration of advanced Virgo and reconstruction of the detector strain h(t) during the observing run O3

“…This technique has been used as an independent cross-check of the PCal technique. Similar development has been started in LIGO [23] and KAGRA [24]. This technique is not discussed in this paper, but its results, described in [25], are consistent within 3% with the PCal-based calibration, thus compatible with the current uncertainties.…”

Review of the Advanced LIGO Gravitational Wave Observatories Leading to Observing Run Four

“…Newtonian calibrators, which employ rapidly spinning masses near the optics, are also under development [85][86][87]. During O3, a Newtonian calibrator with a quadrupole and hexapole was installed at Hanford, and successfully induced motion on the X-end test mass (ETMX) [88]. Due to problems with precision installation and distance uncertainty analysis, the Newtonian calibrator will not be pursued by LIGO as a precision calibration instrument in O4.…”