Enabling early-warning detection of gravitational waves with improved calibration filter design in Advanced LIGO

Accurate calibration has been a critical component of the new era of gravitational-wave discoveries in the first decade of operations of advanced ground-based interferometric detectors, starting with the discovery of GW150914​​. The calibrated strain data from Advanced LIGO has become available at a lower latency within the first decade of the detector's operation. One of the current limiting factors on the latency of the production of calibrated strain data is from the design of finite impulse response (FIR) filtering used to reconstruct the strain from the interferometer readout. Currently, with linear phase FIR filters, the latency induced from the filters is half the length of these filters (~3 seconds). As we look towards the next observing run with ground-based detectors such as Advanced LIGO, efforts are increasing to incorporate early-warning detection of binary inspiral systems. Our work focuses on improving the calibration filter design specifically between 10 Hz to 500 Hz to improve the possibility of detection pipelines identifying signals long before merger. This will better facilitate rapid responses for early warning alerts and multimessenger observations.