Spectrum of NuSTAR observation 2. Panel a: data from NuSTAR/FPMA (FPMB not shown for clarity), together with the best-fit NPEX model (black). We also show the two components of the NPEX model separately, indicating the soft component with a dashed line and the harder component (for which the photon-index is fixed to −2) with a dotted line. Additionally, we show the model with each CRSF removed in turn (orange and green) and with both removed (magenta). Panel b: residuals in terms of χ for the best-fit model with only 1 CRSF. Panel c: residuals to the best-fit model with 2 CRSFs Panel d: residuals in terms of data-to-model ratio without the 50 keV CRSF. Panel e: residuals without the 35 keV CRSF. Panel f: residuals without both CRSFs. In this panel the non-symmetric shape of the residuals can be clearly seen.