Upper left panel: time–distance map obtained using artificial slit A (see right panels of Fig. 1) in AIA 193 Å data. Lower left panel: similar to the upper left panel but for AIA 171 Å. Black asterisks in upper (and lower) right panel represent the minimum intensity corresponding to the time–distance map shown in the left panels. Overplotted in red is the best-fit exponentially damped sinusoidal curve to the minimum intensity points.