in the catalogue).

-   Flux conversion. A conventional mean flux $(FLUX_{MOS}+FLUX_{pn})/2$ in both bands is computed from count rates via the usual conversion factors CF listed in Table \[TabCF\] with a fixed spectral model ($\Gamma=1.7$, N$_H=2.6\times10^{20}$ cm$^{-2}$).

-   Error computation. <span style="font-variant:small-caps;">Xamin</span> currently does not provide errors on count rates, fluxes, or position. A positional error is computed as a function of count rate and off-axis angle (e.g. Table 4 of @2013MNRAS.429.1652C). Flux errors are computed by calculating the Poissonian error on gross counts[^4] according to the formula of @1986ApJ...303..336G, assuming that the fractional error on rates is the same as that on counts, and propagating them through the CF formula. In Fig. \[FigSigma\] we compare the S/N using the computed flux errors to the <span style="font-variant:small-caps;">Xamin</span> detection statistic. The customary $3\sigma$ and $4\sigma$ levels seem to occur for likelihood levels $\sim$ 65 and 115, higher than those found in the comparison of <span style="font-variant:small-caps;">Xamin</span> 3.2 with the XMDS pipeline given in @2013MNRAS.429.1652C, which only deals with some of the longest exposures in XXL, and uses a different analysis software.

![image](sigmavsml.ps){width="17.0cm"}

Additional steps are performed after the ingestion of the band tables in the database for the preparation of the 