W − θ plane from the full GBM catalog (teal) and the subsample of GRBs best fit by the Band function or a SBPL (purple-yellow). The boxes are the allowed regions for the corresponding physical emission mechanisms. The color of the subsample corresponds to the low-energy index (α) of the spectral fit. The two black dashed lines demonstrate how the W − θ plain evolves for fixed β (big dashes) and fixed α (small dashes).