Rolloff energy E_rolloff vs. post-shock density n_o (left) and shock velocity v_s (right) derived by Williams et al. (2013) adopting a distance of D = 2.3 kpc. The velocities scale linearly with the assumed distance, but the trend of E_rolloff with v_s is independent of distance. Overplotted on the right panel are three curves that represent different dependences of E_rolloff on shock velocity v_s: ﹩{E}_{{\rm{rolloff}}}\propto {v}_{{\rm{s}}}^{2}﹩ (cyan solid line), ﹩{E}_{{\rm{rolloff}}}\propto {v}_{{\rm{s}}}^{4}﹩ (red dashed line), and ﹩{E}_{{\rm{rolloff}}}\propto {v}_{{\rm{s}}}^{7}﹩ (blue dotted line). The former two trends are those expected if the maximum energy of the electrons is limited by the age of the SNR or by the timescale of the radiative losses, respectively. The latter curve represents the loss-limited case if the B-field strength is not constant (and instead B ∝ v_s). The ﹩{E}_{{\rm{rolloff}}}\propto {v}_{{\rm{s}}}^{2}﹩ trend does not match the data, and the age-limited scenario is more consistent with our results. We note that the three n₀ > 1 cm⁻³ points correspond to regions #12, 10, and 21 (in order of increasing n₀). The two v_s ≲ 2200 km s⁻¹ points correspond also to regions #12 and 21, which are located where the forward shock is interacting with the dense clump known as knot g (Kamper & van den Bergh 1978; Ghavamian et al. 2000).