Table 6: Range of the expected $f_{\rm X}/f_{\rm opt}$ flux ratios (min/max value in logarithmic units) for the different object classes and EPIC fields. The X-ray fluxes refer to the full XMM-Newton energy range (0.3-10 keV), while the optical fluxes refer to the Johnson's B ( top) and V ( middle) bands and to the B_j band ( bottom). For each source class the slight differences in the $f_{\rm X}/f_{\rm opt}$ values are due to the different $N_{\rm H}$ of the various EPIC fields, which affects the count-rate-to-flux conversion factor.
Field ID Stars WDs CVs Galaxies Clusters AGN

min/max min/max min/max min/max min/max min/max

1 -3.90/+0.50 +1.00/+2.70 -1.02/+1.42 -0.54/+1.83 +0.38/+2.11 +0.25/+1.72

2 -3.91/+0.49 +0.99/+2.69 -1.02/+1.41 -0.54/+1.83 +0.37/+2.10 +0.26/+1.73

3 -3.93/+0.47 +0.95/+2.65 -1.04/+1.39 -0.55/+1.82 +0.38/+2.11 +0.23/+1.70

4 -3.94/+0.45 +0.89/+2.60 -1.06/+1.38 -0.56/+1.81 +0.38/+2.11 +0.22/+1.69

5 -3.80/+0.60 +1.11/+2.81 -0.91/+1.52 -0.44/+1.94 +0.48/+2.21 +0.35/+1.82

6 -3.81/+0.59 +1.10/+2.80 -0.92/+1.51 -0.45/+1.92 +0.46/+2.19 +0.34/+1.81

7 -3.84/+0.56 +1.04/+2.74 -0.96/+1.48 -0.47/+1.91 +0.46/+2.20 +0.32/+1.78

8 -3.78/+0.62 +1.12/+2.82 -0.90/+1.54 -0.42/+1.95 +0.49/+2.22 +0.37/+1.84

**Table 6:** Range of the expected $f_{\rm X}/f_{\rm opt}$ flux ratios (min/max value in logarithmic units) for the different object classes and *EPIC* fields. The X-ray fluxes refer to the full *XMM*-Newton energy range (0.3-10 keV), while the optical fluxes refer to the Johnson's B ( *top*) and V ( *middle*) bands and to the B_j band ( *bottom*). For each source class the slight differences in the $f_{\rm X}/f_{\rm opt}$ values are due to the different $N_{\rm H}$ of the various *EPIC* fields, which affects the count-rate-to-flux conversion factor.
Field ID	Stars	WDs	CVs	Galaxies	Clusters	AGN
	min/max	min/max	min/max	min/max	min/max	min/max
1	-3.90/+0.50	+1.00/+2.70	-1.02/+1.42	-0.54/+1.83	+0.38/+2.11	+0.25/+1.72
2	-3.91/+0.49	+0.99/+2.69	-1.02/+1.41	-0.54/+1.83	+0.37/+2.10	+0.26/+1.73
3	-3.93/+0.47	+0.95/+2.65	-1.04/+1.39	-0.55/+1.82	+0.38/+2.11	+0.23/+1.70
4	-3.94/+0.45	+0.89/+2.60	-1.06/+1.38	-0.56/+1.81	+0.38/+2.11	+0.22/+1.69
5	-3.80/+0.60	+1.11/+2.81	-0.91/+1.52	-0.44/+1.94	+0.48/+2.21	+0.35/+1.82
6	-3.81/+0.59	+1.10/+2.80	-0.92/+1.51	-0.45/+1.92	+0.46/+2.19	+0.34/+1.81
7	-3.84/+0.56	+1.04/+2.74	-0.96/+1.48	-0.47/+1.91	+0.46/+2.20	+0.32/+1.78
8	-3.78/+0.62	+1.12/+2.82	-0.90/+1.54	-0.42/+1.95	+0.49/+2.22	+0.37/+1.84

Field ID Stars WDs CVs Galaxies Clusters AGN

min/max min/max min/max min/max min/max min/max

1 -4.33/+0.87 +0.65/+3.11 -1.54/+1.63 -0.89/+2.04 +0.07/+2.00 -0.10/+2.25

2 -4.33/+0.86 +0.64/+3.10 -1.55/+1.62 -0.89/+2.04 +0.06/+2.00 -0.09/+2.26

3 -4.35/+0.84 +0.60/+3.06 -1.57/+1.60 -0.90/+2.03 +0.07/+2.00 -0.12/+2.23

4 -4.37/+0.83 +0.55/+3.01 -1.58/+1.59 -0.90/+2.02 +0.07/+2.00 -0.13/+2.22

5 -4.22/+0.97 +0.76/+3.22 -1.44/+1.73 -0.78/+2.15 +0.17/+2.10 +0.01/+2.36

6 -4.24/+0.96 +0.76/+3.22 -1.45/+1.72 -0.80/+2.13 +0.15/+2.08 -0.01/+2.34

7 -4.27/+0.93 +0.69/+3.15 -1.48/+1.69 -0.81/+2.12 +0.16/+2.09 -0.03/+2.32

8 -4.21/+0.99 +0.78/+3.23 -1.42/+1.75 -0.77/+2.16 +0.18/+2.11 +0.02/+2.37

Field ID Stars WDs CVs Galaxies Clusters AGN

min/max min/max min/max min/max min/max min/max

1 -4.19/+0.43 +0.74/+2.65 -1.33/+1.31 -0.81/+1.72 +0.13/+1.91 -0.02/+1.70

2 -4.19/+0.43 +0.73/+2.64 -1.33/+1.30 -0.81/+1.72 +0.12/+1.91 +0.00/+1.71

3 -4.21/+0.41 +0.69/+2.59 -1.35/+1.28 -0.82/+1.71 +0.13/+1.91 -0.04/+1.68

4 -4.23/+0.39 +0.64/+2.55 -1.37/+1.27 -0.82/+1.71 +0.13/+1.91 -0.05/+1.67

5 -4.08/+0.54 +0.85/+2.76 -1.22/+1.41 -0.70/+1.83 +0.23/+2.01 +0.09/+1.81

6 -4.09/+0.53 +0.85/+2.75 -1.24/+1.40 -0.72/+1.81 +0.21/+2.00 +0.07/+1.79

7 -4.13/+0.49 +0.78/+2.68 -1.27/+1.37 -0.73/+1.80 +0.21/+2.00 +0.05/+1.77

8 -4.07/+0.55 +0.87/+2.77 -1.21/+1.43 -0.69/+1.84 +0.24/+2.03 +0.10/+1.82