Magnetic energies and helicities of AR 12734, deduced from NLFF modeling. Volume-integrated (a) total magnetic energy, E, (b) total magnetic helicity, H_V, (c) free magnetic energy, E_F, and (d) magnetic helicity of the current-carrying field, H_J. Different plotting symbols mark time series of NLFF models based on different free model parameter choices. The black solid line represents mean values, and the gray-shaded area indicates the corresponding 1σ-uncertainties (standard deviation). The time cadence of the NLFF model is 12 min around the C1.3 flare, and one hour otherwise. Gray-shaded vertical band marks the extended impulsive phase of the flare, as in Fig. 1.