New Perspectives for Multifrequency GW Astronomy: Strong Gravitational Lensing of GW

Abstract

Direct detection of gravitational waves was for a long time a holy grail of observational astronomy. The situation changed in 2015 with the first ever registration of gravitational wave signal (GW150914) by laboratory interferometers on the Earth. Now, successful operating runs of LIGO/Virgo gravitational wave detectors, resulting with numerous observations of gravitational wave signals from coalescing double compact objects (mainly binary black hole mergers) with the first evidence of coalescing binary neutron star system, elevated multimessenger astronomy to the unprecedented stage. Double compact objects (binary black hole systems, mixed black hole-neutron star systems and double neutron star systems) are the main targets of future ground based and space-borne gravitational wave detectors opening the possibility for multifrequency gravitational wave studies and yielding very rich statistics of such sources. This, in turn, makes possible that certain, non-negligible amount of double compact objects will have a chance of being strongly lensed. In this paper we will discuss new perspectives for future detections of gravitational wave signals in the case of strong gravitational lensing. First, the expected rates of lensed gravitational wave signals will be presented. Multifrequency detections of lensed gravitational wave events will demand different treatment at different frequencies, i.e. wave approach vs. geometric optics approach. New possibilities emerging from such multifrequency detections will be