Observed time-integrated spectra fitted with different spectral models. Top panels: X-ray spectra (black dots; the data were grouped to at least one count per bin), in units of counts (cts s⁻¹ keV⁻¹). We also plot the best-fit PO (blue lines), BR (orange lines), and BB (green lines) spectral models; see Table 5 for the corresponding best fitting parameters. Bottom panels: residuals (defined as data-model normalized by the uncertainty; (D − M)/σ) of each spectral model.