SPI spectral response to the DDT1p4 model during revolutions 1380-86. The dotted and dashed lines represent the contribution of the diagonal and off-diagonal terms of the convolved spectrum, respectively. The solid line is the sum of both components. The diagonal component scales with the original model, while the non-diagonal component is produced by the energy redistribution of high energy photons and contributes to the continuum with an amount comparable to that of the diagonal component in the 100−200 keV range.