Amplification factor (f_a) profiles (points with 1σ error bars) obtained from the spectral analysis of bursts 4 (left), 6 (middle), and 23 (right) of 4U 1636-536. For the longer burst 4, the first 30 s of the f_a profile have been magnified for better comparison. The dashed lines correspond to the burst light curves, and the horizontal dotted lines to f_a = 1.