I_P ∝ F_SXR relations for the four integral energy bands of the SEP events: E  >  10 (top left); E  >  30 (top right); E  >  60 (bottom left); and E  >  100 MeV (bottom right). The estimated SXR flare mean values for the events of 23 February 1956 and AD774/775 are represented as purple and cyan filled circles, respectively. The plotted SXR intensities were obtained by dividing the values in Appendix C by 0.7 to reflect the recent NOAA recalibration (Hudson et al., in prep.; Cliver et al. 2022).