Upper panel: GOES 0.5–4 Å and 1–8 Å light curves and temporal evolution of RESIK flux in the 3.33 Å–4.32 Å wavelength range. The GOES fluxes should be referred to the left-hand y-axis, the RESIK fluxes to the right-hand y-axis. Lower panel: RHESSI light curves of five energy bands between 4 and 300 keV taken during the 20 September 2002 flare. The grey box indicates the time interval from which the observations were used for the analysis.