Time-resolved spectroscopy using the f_a model for burst #4. Results for other bursts are shown in Fig. A.2. Gray markers are used for the blackbody model, and magenta markers are used for the first f_a case, constant*(diskbb+comptt), and cyan markers for the second f_a case, constant*diskbb+comptt. Since their behavior is similar, the magenta markers overlap the cyan ones. Panel a shows the estimated bolometric flux, panel b shows the time evolution of the blackbody temperature, panel c shows the time evolution of the blackbody normalization, panel d shows the evolution of the f_a factor, and panel e gives the reduced χ² fit statistic. Time is relative to the burst onset (t₀).