Dependence of three central (merger or accretion) shock quantities on upstream Mach number ℳ_u and adiabatic index γ, as derived from the Rankine–Hugoniot jump conditions in ideal gases. Radiation from ℳ_u < 10 shocks is predominantly generated by electrons that stem from the ICM, whilst radiation from ℳ_u > 10 shocks is predominantly generated by electrons that stem from the WHIM. Top: the spectral index α of angularly unresolved shocks, assuming standard DSA. Middle: the downstream-over-upstream plasma density ratio. Bottom: the downstream-over-upstream plasma temperature ratio.