that observed below 1500 CU of FIMS intensity (blue) corresponds to the regions of arc B and the lower part of arc A, where two-photon emission, not considered in the simulation, is a significant contribution. If the difference is regarded as the contribution from two-photon emissions, the amount is estimated to be $\sim$25-40$\%$ of the total observed continuum, a little lower than the previous value of $\sim$50-70$\%$ in @jo11, which was obtained by converting the observed H$\alpha$ intensity assuming that 1 Rayleigh of the H$\alpha$ line corresponded to the two photon emission of 60 CU.

Large fluctuations are seen between 1500 and 2500 CU of FIMS intensity (sky-blue), and the simulation result is considerably lower than the observed one above 2500 CU of FIMS intensity (orange). These discrepancies may originate from local variations of the simulation parameters such as the distance to the front face and the thickness of the dust cloud. More consideration of these discrepancies will be given in the Discussion section.

Figure \[fig:contour\] shows the contour maps for the 90 $\%$ confidence ($\Delta\chi^2$ $\sim$ 1.06) among the four variables, the albedo, the *g*-factor, the distance to the front face of the slab, and the thickness: the ranges 