Space-time diagram of the m = 1 mode of the Fourier transform of the θ-integrated density with respect to the azimuth φ for model A. Panel b is obtained with a much larger time resolution than panel a, such that high frequency fluctuations are well resolved. On panel b, we see the overdensity generated at early time (t ≃ 147 P_orb) propagating outward and expanding radially, and a new lump building up from t ≃ 152 P_orb.