Notes. The parameters x and y are centroid coordinates with respect to the bottom left corner of our cutout, q is the axis ratio, θ is the position angle measured counterclockwise from the x-axis, θ_E is the Einstein radius, r_c is the core radius, γ′ is the slope, γ_ext is the external shear magnitude, and ϕ_ext is the external shear orientation. The constraints for this model are the selected multiple image systems. The best-fit model has an image position χ² of 12.6.