Lens system configuration according to the 2L1S model. The concave curve represents the caustic, the line with an arrow is the source trajectory, and the filled dots marked by M₁ and M₂ indicate the positions of the lens components. The caustic of the standard model are drawn in gray. For the higher-order model, in which the lens position and caustic vary in time because of the lens orbital motion, we mark the lens and caustic at two epochs of HJD′ = 9323 (marked in blue color) and 9334 (in red color). The source trajectories of the standard and higher-order models are drawn in gray and black. The inset shows the zoom-in view of the region around M₁. The coordinates are centered at the photocenter and lengths are scaled to the angular Einstein radius corresponding to the total mass of the lens. The dashed unit circle centered at the origin represents the Einstein ring.