On the Determination of Mass Density Profiles for Gravitational Lenses from Gravitational Wave Data

As the network of ground-based detectors becomes more sensitive, the gravitational lensing of binary black hole or neutron star merger will become increasingly likely - and will offer both an important further probe of strong gravity and a novel means of constraining the properties of the lens. There is a reasonably mature prior literature exploring the theoretical signatures of lensed gravitational-wave sources, and the LIGO Virgo KAGRA (LVK) Collaborations have already invested significant effort in setting up analysis pipelines to search for lensed signals, with several short-author or collaboration papers presenting the results of those searches.

Much of the code infrastructure has focussed on point-mass lenses, however, particularly for microlensing events. While that is partially justified as a reasonable assumption, the opportunity to compare results for different extended lens mass distributions is an important and timely one.

The aim of this project is to develop new analysis approaches that consider different lens models, efficiently compute their lensing amplification functions and permit a Bayesian model comparison of their relative applicability to candidate signals. The codes to carry out these calculations will be incorporated into the LVK lensing pipelines, thoroughly tested and applied to data from future LVK observing runs.

Wider applicability of the lensing codes to e.g. data from 3rd generation ground-based detectors will also be explored. The ultimate goal of this work will be to allow a more robust detection of a lensed gravitational-wave event and a more complete investigation of the lens properties.