The Advanced Virgo Photon Calibrators

TL;DR

This paper discusses the implementation and calibration of photon calibrators in Advanced Virgo, improving the accuracy of gravitational wave detector calibration and reducing systematic biases for better scientific results.

Contribution

It introduces the use of photon calibrators in Advanced Virgo and details the intercalibration process with LIGO, achieving a systematic bias reduction and setting a path for improved future calibration accuracy.

Findings

Systematic bias of 3.92% removed through intercalibration.

Calibration uncertainty estimated at around 1.36-1.74% during O3.

Expected to reduce calibration uncertainty below 1% in future runs.

Abstract

As the sensitivities of LIGO, Virgo and KAGRA detectors improve, calibration of the interferometers output is becoming more and more important and may impact scientific results. For the observing run O3, Virgo used for the first time photon calibrators (PCal) to calibrate the interferometer, using radiation pressure of a modulated auxiliary laser beam impinging on the Advanced Virgo end mirrors. Those optical devices, also used in LIGO, are now the calibration reference for the global gravitational wave detectors network. The intercalibration of LIGO and Virgo PCals, based on the same absolute reference called the Gold Standard, has allowed to remove a systematic bias of 3.92% that would have been present in Virgo calibration using the PCal. The uncertainty budget on the PCal-induced displacement of the end mirrors (NE and WE) of Advanced Virgo has been estimated to be 1.36% for O3a and 1.40% on NE PCal (resp. 1.74% on WE PCal) for O3b. This uncertainty is the limiting one for the global calibration of Advanced Virgo. It is expected to be reduced below 1% for the next observing runs.