Top panel: Normalized LC for q = 1, b = 20 M, seen at an inclination angle i = 70°. Two modulations dominate the LC, at the semi-orbital period and at the lump period. Middle panel: Density map in the (t, r)-plane for φ = 3π/2 (φ = 0 being the line of sight, it maximizes the Doppler effect) over the same period. Bottom panel: Amplitude of the Fourier modes in the LC, dominated by the lump modulation, and zoom-in view on the binary-lump beat signal, divided over a frequency interval, and the semi-orbital modulation. They are shown in power for clarity and are compared to a background red-noise fit of the form ω^−α with α ∼ 2.