Left panel: 400 SEDs at 294 days (red line) and 323 days (purple line). The stars show data for each epoch and the error bars are smaller than the marker size. Middle panel: model light curves for 400 randomly selected parameter sets from an MCMC for Model (B). Data are the same as those in Figure 2. The decline index α between 260 and 300 days is annotated. Right panel: zoom-in of the optical data and light curves between 100 and 400 days post GRB 170817A/GW170817.