The First Model-independent Chromatic Microlensing Search: No Evidence in the Gravitational Wave Catalog of LIGO–Virgo–KAGRA

Abstract The lensing of gravitational waves (GWs) due to intervening matter distribution in the Universe can lead to chromatic and achromatic signatures in the wave-optics and geometrical-optics limit, respectively. This makes it difficult to model the unknown mass distribution of the lens and hence requires a model-independent lensing detection technique from GW data. We perform the first model-independent microlensing search in the wave-optics limit on the 72 superthreshold GW events observed with both the LIGO detectors up to the third observation catalog, GWTC-3 of LIGO–Virgo–KAGRA, using the analysis method μ - GLANCE . These unmodelled searches pick up one plausible candidate, GW190408_181802, with a slightly above-threshold residual amplitude compared to the residual expected from detector noise. However, exploring the microlensing modulation signatures on this event, we do not find any conclusive evidence of the microlensing signal in the data. With this, we confidently rule out the presence of any statistically significant microlensing signal in the 72 events up to GWTC-3 in a model-independent way.