Corrected invariant mass spectrum for the coherent four-pion photoproduction fitted to the model described by a single resonance and an alternative shape of the non-resonant production given by Eq.A.2.. Black error bars represent the statistical uncertainty, the orange band shows the uncorrelated systematic uncertainty, and the boxes show them added in quadrature. "Prob'' reflects the probability of obtaining the given or a higher $\chi^2/\mathrm{ndf}$ of the fit.