| dc.description.abstract | The coalescence of binary black holes produces gravitational waves, which subsequently can be gravitationally lensed (like light) when passing by massive astrophysical objects, such as galaxies. We observe strong lensing as the occurrence of repeated events (images) with different amplitudes, arriving at different times at our detectors due to travelling along different trajectories.
We build a population of strongly lensed gravitational waves, based on analyses of binary black hole detections and on electromagnetic observations of strong lensing. We investigate the predicted rate of galaxy-lensed event detections for the ground-based LIGO-Livingston, LIGO-Hanford, Virgo and KAGRA gravitational wave detectors, and we forecast ~ 1-2 lensed events per year at their design sensitivities. We also show the event rates for the future LIGO detector upgrades A+ and Voyager, and comment on possible improvements by including so-called sub-threshold triggers – gravitational waves buried in noise.
We find most lensed binaries at redshifts z ~ 1-4, beyond the regular detector horizon. We report the predicted distributions for lensing parameters, such as the time delay between images. We discuss the impact of lensing statistics on lensed event searches, which rely on comparing pairs of event triggers. However, two unlensed events can have a similar signature within detector accuracy, producing a false alarm. We find that including lensing statistics can improve the significance of a truly lensed event by a factor ~ 30. We argue that the inclusion of lensing statistics is vital for the lensed event searches, as otherwise the occurrence of a false alarm becomes inevitable for long observing runs. We hope that this work will further the case for lensed event searches, and we stress the importance of incorporating lensing statistics into these searches. | |
