Comparison of the mean temporal indices of the off-axis afterglow light curves of the analysed GRB sample observed at different viewing angles (dotted, dashed, and dot-dashed lines) with the observed temporal indices of each FXT (red and purple points). The first and fourth panels show example light curves at different viewing angles for a uniform and a structured jet with θ_W = 2θ_C, respectively, and the Chandra flux limit (converted to a luminosity limit in this case, assuming a photon index of Γ ≈ 2 and a redshift of z = 0.2851) is drawn arbitrarily at L_{0.3 − 10 keV} = 10⁴² erg s⁻¹, for illustrative purposes. The results are shown for the uniform-jet case (second panel) and the structured-jet case (third panel). The horizontal lines (plus 16th – 84th percentile uncertainty regions) correspond to the mean slopes of the off-axis GRB afterglow light curves computed during three different times: before the time of the peak in the case of a uniform jet or before the transition time in the case of a structured jet (α_rise, dotted lines), the part between the peak time or transition time and the jet-break (α_intermediate, dashed lines), and the post-jet-break decay (α_decay, dot-dashed lines). They are plotted at different viewing angles, corresponding to the colours in the colour bar on the right. A black dashed line marks a flat slope with α = 0. Also shown are the FXTs that are fit by a power law with temporal index α (red open circles) and the FXTs that are fit by a broken power law with temporal indices α₁ (red points) and α₂ (purple points) before and after the break, respectively.