Example of the fitting of the modified Band function (Eqs. (1) and (2)) to the data points (Sect. 3) for GLE #43, 19-Oct-1989. Blue crosses and vertical lines denote the high-energy NM data with uncertainties, and the upper limits, respectively (Usoskin et al. 2020a), while red circles correspond to low-energy data from GOES-6 (see Table 1). The grey line with shading depicts the best-fit MBF, along with its 68% confidence interval.