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tokens: sets in some specific cases – in particular in the second outermost shell when using projct . We speculate that these discrepancies may be due to a combination of remaining calibration issues and artifacts propagated when projct is used. Nevertheless, in both cases the deprojected EPIC spectra clearly reveal the presence of central drops for the Fe, Si, S, Mg and Ca abundances. Despite the formal consistency reported above, we note that the uncertainties of the XMM-Newton abundances of Ar and Ca are much larger than the uncertainties of the Chandra measurements. This point is discussed in more detail in Sect. 3.5 . 3.5. Broad-band versus narrow-band fits Whereas fitting the spectra using the full energy band (i.e., typically ∼0.5–7 keV for Chandra ACIS) is the standard procedure for deriving the best-fit parameters, this approach may bias the metal abundance measurements. In fact, since the abundance of a given element is directly proportional to the equivalent width of its line (namely, the ratio between the total line flux and the continuum flux at the centroid energy of the line), incorrect determination of the continuum in the vicinity of the line would lead to incorrect measurement of the corresponding elemental abundance. Because no instrument is calibrated with infinite precision, some slight imperfections of the effective area may produce these local over- or underestimates of the continuum. In the case of very deep observations, that is, when statistical uncertainties become smaller than the above systematic effect, such a bias may become highly significant (e.g., Mernier et al. 2015 ; Simionescu et al. 2019 ). A good way to minimize such biases is to refit the spectra between several local energy bands, each of them including the K-shell emission line(s) used to derive the abundance of a given element as well as part of the surrounding continuum. In these “narrow-band” fits (by contrast to the above “broad-band” approach), the only parameters that were kept free were the (local) normalization and the abundance of the considered element. All the other parameters were fixed to the best-fit value of the broad-band fit. A comparison of the resulting narrow-band fit profiles with the ones obtained using broad-band fits (assuming a vgadem model and using dsdeproj ) is shown in Table 2 and Fig. 4 . We used the 1.5–2.8 keV energy range for Si and S, 2.9–3.5 keV for Ar, 3.3–4.3 keV for Ca, and 5.0–7.0 keV for Fe. Fig. 4. Deprojected profiles of Fe, Si, S, Ca, and Ar abundances, and the Ar/Fe (Fe taken from the broad-band fits) ratio, using broad- (red) and narrow-band (blue) fits, obtained using the vgadem model and the dsdeproj deprojection method. All errors are quoted at the 68.27% (1 σ ) confidence level based on . The blue data points have been shifted slightly on the X-axis for clarity. The narrow-band Fe profile in Fig. 4 is consistent with the broad-band profile and also shows a drop in the innermost two bins (at r ≲10 kpc). The