Probing the spin of compact objects with gravitational microlensing of gravitational waves

TL;DR

This paper investigates how gravitational wave signals affected by microlensing by rotating compact objects can reveal the properties of these lenses, especially their spin, using future detector observations.

Contribution

It introduces the first waveform models for microlensed GWs by rotating lenses and demonstrates parameter inference capabilities for such lenses with future detectors.

Findings

Lens parameters are well recovered at 90% confidence for SNR 50.

Parameter estimation improves significantly at SNR 100.

Method can distinguish rotating lens properties in wave-optics regime.

Abstract

Propagating gravitational waves (GWs) can encounter a massive object (lens) whose gravitational radius is comparable to the wavelength of the GWs (wave-optics regime). The resulting `microlensed' signal contains imprints about the properties of the lens. In this work, we compute the GW waveforms microlensed by a rotating compact object in weak-field gravity. Using these waveforms, for the first time, we assess how well the parameters of the rotating lens can be inferred from GW lensing observations. We find that if we allow for naked singular solutions within general relativity or beyond, which in principle can have spins that are not bounded to be extremal, our method can be used to extract the rotating lens parameters using observations of microlensed GWs with future detectors. As a result, we find that the lens parameters for such lenses are well recovered within $90\%$ confidence for signal-to-noise ratio (SNR) 50 and especially well for SNR$=100$ with Einstein Telescope.