Temporal decay indices α₂ vs. α₁ for our samples (excluding the internal plateau bursts). The three solid lines indicate the closure relations of three specific external shock models invoking energy injection with the parameter q = 0, as is expected in the BH/magnetar central engine models. The red, black, and blue solid lines are the models α₂ = (3α₁ + 3)/2 (ν_m < ν_x < ν_c; ISM); α₂ = (3α₁ + 1)/2 (ν_m < ν_x < ν_c; wind); and ﹩{\alpha }_{2}=(3{\alpha }_{1}+2)/2\,({\nu }_{m}\lt {\nu }_{x}\lt {\nu }_{c}﹩; ISM and wind).