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We report a discovery of a double radio relic in the cluster mergerZwCl1447.2+2619 ($z=0.376$) with uGMRT observations at $420\rm~MHz$ and$700\rm~MHz$. The linear sizes of the northern and southern relics are$\sim0.3~$Mpc and $\sim1.2~$Mpc, respectively, which is consistent with thetheoretical expectation that a larger relic is produced in the less massivesubcluster side. However, ZwCl1447.2+2619 is unlike other known double radiorelic systems, where the larger relics are much more luminous by severalfactors. In this merger the higher surface brightness of the smaller northernrelic makes its total radio luminosity comparable to that of the much largersouthern relic. The surface brightness ratio $\sim0.1$ between the two radiorelics differs significantly from the relation observed in other double radiorelic systems. From our radio spectral analysis, we find that both relicssignify similar weak shocks with Mach numbers of $2.9\pm0.8$ and $2.0\pm0.7$for the northern and southern relics, respectively. Moreover, the northernrelic is connected to a discrete radio source with an optical counterpart,which indicates the possible presence of cosmic ray injection andre-acceleration. Therefore, we propose that this atypical surface brightnessratio can be explained with the particle acceleration efficiency precipitouslydropping in the weak shock regime and/or with re-acceleration of fossil cosmicrays. Our multi-wavelength analysis and numerical simulation suggest thatZwCl1447.2+2619 is a post-merger, which has experienced a near head-oncollision $\sim0.7\rm~Gyr$ ago.

Discovery of a double radio relic in ZwCl1447.2+2619: A rare testbed for shock acceleration models with a peculiar surface brightness ratio