Time-resolved spectral analysis of GRB 080916C. The upper-left panel shows the fit of the LAT light curve (0.1–10 GeV) with the model from Eq. 1, along with GBM light curves (BGO and NaI). The middle panel compares the inferred spectral index (ϕ) with the observed spectral index, with the shaded grey area representing uncertainties on the predicted index, derived from the decay temporal index fit. The bottom panel shows the residuals, indicating the deviation of the light curve from the model. The remaining panels show the time-resolved spectral fits. Details are provided in Table A.1.