Non-relativistic and relativistic magnetic reconnection with the effects of optically thin synchrotron cooling

We performed special relativistic resistive magnetohydrodynamic simulations of Petscheck-type magnetic reconnection including an optically thin synchrotron cooling. The magnetization parameter, σ₀, which is the ratio of Poynting flux to mass flux in the upstream plasma, is taken to be 0.01 and 3. For the non-relativistic plasma (σ₀ = 0.01), the radiative cooling subtracts thermal energy mainly in the upstream plasma and a plasma is strongly compressed at the slow shock. The cooling in the post-shock region and plasmoid also reduces the thermal energy and it forms a narrower outflow. The reconnection rate slightly increases as a result of the radiative cooling, since the plasma beta in the inflow region becomes small. The effect of decreasing thermal energy in the outflow region is more prominent for the relativistic plasma (σ₀ = 3). In this case, the outflow temperature increases and the plasma internal energy becomes comparable to the plasma rest mass energy. The subtraction of this thermal energy by radiative cooling leads to a decrease in plasma inertia and the outflows are more accelerated than without radiative cooling. The reconnection rate is also enhanced by its Lorentz contraction effect. For both non-relativistic and relativistic simulations, it is concluded that the reconnection rate is determined by the plasma beta in the inflow region.