Programme by Session

In the early 2020s the rate of detection of strongly-lensed gravitational waves will approach and soon surpass ~1 per Earth year. On a similar timescale, LSST will begin surveying the Southern sky and will thus provide a data stream within which to search for electromagnetic (EM) counterparts to lensed GW sources (irrespective of any lensing effects). It is important to consider how to optimise such a search for EM counterparts to GW sources, and in particular whether/how to go about building up our knowledge of the population of lensing galaxy clusters to facilitate that search. Conventional lens searches utilise EM observations of lensing phenomena (such as bright arcs) caused by background galaxies or quasars. This strategy relies on a chance alignment between a source and the strong-lensing cross-section of a lens, and on the lensed source being detectable. Such a source-based search could therefore miss an unknown and potentially large fraction of the lens population that is relevant to the lensing of GWs. I have developed an analytic model to estimate the fraction of lenses that source-based lens searches will miss as a function of the lens mass, concentrating on the galaxy group and cluster mass range. I will present the details of the model, an application of it to an LSST-like survey, and discuss its implications for the potential first detection of lensed GWs.