Best-fitting simulated light curves. We show here the best-fitting R and V simulated microlensing light curves (red and blue curves) from the 25 tracks with the smallest χ² = χ_R² + χ_V² for the Gaussian disc model (left) and the Shakura-Sunyaev thin disc model (right). The data points are the measured R (orange circles) and V (purple squares) B − C difference curves (i.e. the two uppermost curves on the right side of Fig. 2 inverted and with adapted error bars as described in Sect. 3.2) as used for the χ² calculation.