Search for dark matter using the phenomenon of strong gravitational lensing

We provide a brief overview of the methods for estimating the dark matter content in the Universe based on the phenomenon of strong gravitational lensing—the method of macroimage flux ratio anomalies and the method based on an analysis of the probability distribution for the magnification of macroimages due to microlensing events. Both methods require the specification of a macrolens model, knowledge of the spatial structure or at least the effective size of the source, and numerical simulation of microlensing events followed by a comparison of the simulation results with observational data. Using the quadruply lensed quasar Q2237+0305 as an example, we show the effect of the spatial source structure on the shape of the magnification probability distribution in microlensing events. We also point out the need to take into account the contribution from the intrinsic quasar variability to the observed light curve and to develop a physically justified algorithm to fit the observational data. For the first time, based on all the available observations of Q2237+0305, we have constructed the magnification probability histograms for all four macroimages. We analyze the possibility of using them to estimate the content of continuously distributed (dark) matter in the galaxy Q2237+0305 at a distance from its nucleus that corresponds to the macroimage locations.