XMM 2018 EPIC-pn spectrum of Q2237. Panel a: XMM 2018 data (black) and best-fit model (solid blue line) with Model pl_pca_el. The dashed blue line indicates the emission line at E_rf = 6.84 ± 0.11 keV. Panel b: XMM 2018 best-fit residuals for Model pl. Panel c: XMM 2018 best-fit residuals for Model pl_pca_el. The data are grouped to obtain at least 20 cts/bin, with the minimum energy width set to one third of the CCD energy resolution. The best-fit parameters are summarized in Table 6. Due to background-dominated bins above 7.0 keV, we restricted the fitting to the 0.3–7.0 keV observed-energy range (1–19 keV rest-frame energy range).