Panels a) to c), top: reconstructed X-ray spectra and fitting results. The three examples shown here were selected at the rising phase, the HXR peak, and the decay phase. These spectra were derived from detector 4 with 20 s integration time (histogram) and fitted with an isothermal component (green, dot-dashed line) and a nonthermal thick-target model (blue, dashed line). A second isothermal component (red, solid line) was added when necessary for a better fit. The gray curves represent the background. The obtained parameters, such as reduced chi-square, plasma temperature T, emission measure EM, power-law distribution index δ of the nonthermal electrons, and low-energy cutoff E_c, are listed in the top right corner of each panel. Panels a) to c), bottom: residuals from the fitting.