Volume-integrated total energy W_tot equals the sum of the energy in relativistic electrons W_e and magnetic field W_B. For any best-fitting set of parameters, the energy partition is a function of the normalisation B₀ of the magnetic field at the shock distance r_s. The best-fitting value is found to be (90% c.l. uncertainty, including systematical uncertainties). This value is slightly smaller than the minimal energy configuration at B₀ = 514 μG.