Microlensing simulation for HE 0435−1223. Magnification maps of images A (top left) and B (middle left) are generated using microlenses with ⟨M_*⟩ = 0.2 following the Salpeter initial mass function within the mass range of 0.06 M_⊙ and 6.46 M_⊙. The convolved maps of images A (top right) and B (middle right) are obtained with a Gaussian kernel for the source half-light radius as listed in Table 1. Each map has 57.3 × R_E on a side (or 2000 pixels). A few trajectories (white lines) are randomly drawn with a transverse velocity of 600 km s⁻¹ and a length equal to the observational duration (5338 days). A pair of simulated light curves (red circles) is shown on the bottom panel. The corresponding difference light curve δm yields the microlensing amplitude Δm ≈ 0.75 mag, following our definition in Sect. 3.