FWHM_min versus the initial Lorentz factor Γ₀ for a number of Type-II GRBs, with the predictions discussed by Xie et al. (2017), highlighted by the light shaded region between dash-dotted lines ( annihilation mechanism) and by the dark shaded region between dashed lines (BZ mechanism). Left: same as Fig. 13. Right: same as Fig. 9, except that the two axes are swapped for ease of comparison with the expectations discussed by Xie et al. (2017).