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.

Toward Calibration of the Global Network of Gravitational Wave Detectors with Sub-Percent Absolute and Relative Accuracy

“…Thus this system can simultaneously produce time varying forces at twice and three times the Ncal rotation frequency. During the third observing run, using the LIGO Hanford detector, it was demonstrated that a calibrated displacement well above the detector sensitivity could be generated using this system with measurement uncertainty at the 1% level [31].…”

“…The force produced by such a system is dependent on the known gravitational constant, the distance between the rotating masses and the detector test mass and the geometrical configuration of the system, shown schematically in Figure 2. Such systems have been developed and tested within the Virgo [28,29], KAGRA [30], and LIGO [31] projects during the last few years and have shown promise for providing absolute fiducial displacment with uncertainty better than 1%.…”

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.…”

Calibration Uncertainty's Impact on Gravitational-Wave Observations

“…[12,13] and references therein). Recently, several authors have investigated Newtonian calibrators [14,15], which drive the test masses through the Newtonian gravitational force exerted by an oscillating mass multipoles (rotating dumbbell). Additionally, several authors have studied the ability of astrophysical signals themselves to calibrate detectors.…”