tokens: for each of the late-phase loops, the energy input in late-phase loops reaches ∼7.7 × 10 29 erg. For the main flaring loops (as mentioned in Sect. 3.1 ), both of the two-stage energy release processes contribute to the heating. Hence, the heating duration of the main flaring loops is double compared with the late-phase loops. Assuming that the amplitude of heating rate is equal to H 0 , the energy input in the main flaring loops is estimated to be (1.5−3.8) × 10 29 erg. Based on the EBTEL simulation, the energy input in the post-flare loops amounts to (9.2−11.5) × 10 29 erg. 3.6. Nonthermal energy in flare-accelerated electrons Under the thick-target assumption ( Fletcher et al. 2013 ), HXR emissions at the footpoints are produced by collisional bremsstrahlung during the passage of flare-accelerated nonthermal electrons through a dense target, where the electrons are stopped by Coulomb collisions and lose energy in the chromosphere. The localized plasma can be heated up to ∼10 MK accompanied by chromospheric evaporation and condensation ( Tian et al. 2014 ; Li et al. 2015 ; Zhang et al. 2016a , b ; Zhou et al. 2020 ). The distribution of injected nonthermal electrons above a low-energy cutoff ( E c ) is assumed to be in the form of single power law with a spectral index of δ , , where A 0 is a normalized parameter of the total electron flux (in units of 10 35 electrons s −1 ). In Fig. 6 , three characteristic HXR spectra made from detector 9 of RHESSI during the first stage of energy release are displayed. In each panel, the fitted thermal component is drawn with a red line, while the nonthermal component is drawn with a blue line. It is obvious that the isothermal temperatures from RHESSI are close to those derived from GOES. Fig. 6. Three characteristic HXR spectra with an integration time of 20 s (black lines) and the fitted thermal (red lines) and nonthermal (blue lines) components. T e and EM of the thermal component are labeled. The low-energy cutoff ( E c ), spectral index ( δ ) of nonthermal electrons, and of the residuals are also labeled. The delivered energy by nonthermal electrons above E c is calculated by integrating the injected power during 12:40−12:46 UT, where A nt is the electron injection area, E H is set to be 30 MeV ( Warmuth Mann 2016a ). The nonthermal energy in flare-accelerated electrons during the first stage is estimated to be ∼1.74 × 10 30 erg. Considering that the HXR observation from RHESSI was unavailable during the second stage of energy release around 12:47:30 UT, it is impossible to calculate the nonthermal energy of electrons from RHESSI during the second stage. In Fig. 2 b, the second peak of GOES derivative accounts for ∼1/4 of the first peak, implying that energy input during the second stage accounts for ∼1/4 of the first stage. In this way, the nonthermal energy in the flare-accelerated electrons during the second stage is crudely estimated to be 0.44 × 10 30 erg. Therefore, the total nonthermal energy
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