Top panels: NuSTAR spectra of Ser X-1 and best-fitting model together with residuals in units of sigma for the corresponding model. These are; top-left: “rdb-reflio-pl”, top-right: “rdb-rfxconv-pl”. Bottom panels: XMM-Newton spectra and best-fitting model together with residuals in units of sigma for the corresponding model. These are: bottom-left: “diskline-pl-xmm”, and bottom-right: “rdb-rfxconv-pl-xmm”. For clarity, only the first XMM-Newton observation is shown. Dashed lines indicate the black-body component, dotted lines indicate the reflection components (i.e., the Diskline profile for the iron line or the self-consistent reflection component), the solid line indicates the power-law component, and the dashed-dotted lines indicate the comptonized component.