Left: radio color-color plot of the main relic R1, superimposed with the JP (blue dash-dotted line), KGJP (green dash-dotted), and CI (red dash-dotted) spectral aging models adopting α_inj = −0.67. The observed data points seems to be relatively consistent with the JP model, suggesting that the relic is very likely seen close to edge-on. To extract spectral index values, we create square-shaped boxes with a width of 10″, corresponding to a physical size of about 45 kpc. Right: particle acceleration efficiency of the main relic R1 as a function of magnetic field. The values are estimated using the Mach number of ℳ = 3.6 (α_int = −1.17) and Ψ(ℳ, T_d) = 0.193. The required acceleration efficiency is about 1% or below, which can be achieved by accelerating electrons from the thermal pool if the magnetic field is sufficiently strong and a large fraction of the shock shows high Mach number.