Confirmation of the Finch Flatter-Fainter Relation for the Quadruple Images of Lensed Point Sources

Abstract

Finch et al (2002) derived relations for the summed absolute magnifications of quadruply lensed images that vary inversely with flattening in two alternative isothermal gravitational potential models. However, they did not elaborate on the selection effects this "flatter-fainter'' relation induces in actual lensed systems. We test the relation against the Luhtaru et al (2021) sample of 39 quadruply lensed quasars (38 of which we model successfully), using predicted rather than observed magnifications to avoid the complication of microlensing. We found that the summed predicted magnification decreases by a factor of ten over the observed range of flattening.