Spectral energy distribution of 4U 0115+63. Panel (a): Unfolded EF_E spectra during XMM-Newton observations Obs1 (black), Obs2 (blue), and Obs2016 (red) and fitted jointly. The dashed black curve represents the bbodyrad component. The dotted gray line shows a possible additional hard component, and the solid gray line indicates the total model spectrum. As a comparison, the spectrum of Obs3 is also in orange, and its low-energy part (< 1 keV) is excluded to simplify the panel. Residuals from the spectral fits using the bbodyrad and the bbodyrad + gaussian models are shown in panels (b) and (c), respectively. Panels (d), (e), and (f) show the residuals for Obs1, Obs2, and Obs2016, respectively, using the pegpwrlw model.