Table 7: Main characteristics of the X-ray sources with no candidate optical counterpart and $\log(f_{\rm X}/f_{\rm opt})\protect \ga 2$.
(1) (2) (3) (4) (5) (6) (7) (8)
OBS SRC DETECTION BANDS $kT_{\rm br}$ $kT_{\rm bb}$ $\Gamma$ Flux $f_{\rm X}/f_{\rm opt}$
    (keV) (keV) (keV)   (10-14 cgs) (log)
2 XMMU J061807.6-331237 0.5-1 $\le $5 0.2 $\ge$1 2.28 $\pm$ 1.23 1.73 $\pm$ 0.31
3 XMMU J061429.8-333225 0.5-2; 0.5-1; 1-2 $\ge$2 0.5 1-2.5 12.92 $\pm$ 3.67 2.48 $\pm$ 0.24
3 XMMU J061450.2-331501 0.5-2; 1-2 2-5 >0.2 1.5-2 5.14 $\pm$ 2.21 2.08 $\pm$ 0.27
3 XMMU J061526.1-331724 0.5-2; 1-2 $\ge$2 >0.2 1-2 3.22 $\pm$ 1.12 1.88 $\pm$ 0.25
3 XMMU J061546.9-333347 1-2 $\ge$1 $\ge$0.2 $\le $2.5 1.93 $\pm$1.03 1.66 $\pm$ 0.31
4 XMMU J061507.9-330026 0.5-2; 2-10; 1-2; 2-4.5 >5 >0.5 $\le $1 3.67 $\pm$ 1.18 1.93 $\pm$ 0.24
4 XMMU J061557.2-324635 0.5-2; 1-2 0.5-5 0.2-0.5 2-2.5 2.95 $\pm$ 1.47 1.84 $\pm$ 0.29
4 XMMU J061504.5-330533 0.5-2 $\le $5 >0.2 $\ge$1.5 2.06 $\pm$ 1.41 1.68 $\pm$ 0.36
8 XMMU J124642.5-832212 2-10 >5 >0.5 <1 3.62 $\pm$ 1.69 1.77 $\pm$ 0.20
Key to Table - Col. (1): EPIC field sequential reference number. Column (2): Source identification. Column (3): Source Detection Bands, i.e. the energy ranges j where the probability P(j) that the source counts are due to a background fluctuation is lower than $2 \times 10^{-4}$ (see text). Column (4): Estimated range of possible $kT_{\rm br}$ temperatures for a thermal bremsstrahlung spectrum (i.e. XSPEC wabs bremss model) compatible with the measured HRs. Col. (5): Estimated range of possible $kT_{\rm bb}$ temperatures for a thermal blackbody spectrum (i.e. XSPEC wabs bbody model) compatible with the measured HRs. Column (6): Estimated range of photon index $\Gamma$ values for a power law spectrum (i.e. XSPEC wabs pow model) compatible with the measured HRs. In all cases, we assumed the galactic $N_{\rm H}$ estimated in the pointing direction (Table 1). The wide range of values for the spectral parameters $kT_{\rm br}$, $kT_{\rm bb}$ and $\Gamma$ are due to the low count statistics and to the large error bars on the derived source HRs. Column (7): Estimated source flux in the energy range 0.3-10 keV, assuming a power law spectrum with $\Gamma = 1.7$ and the galactic $N_{\rm H}$ in the pointing direction. Column (8): Lower limit (in logarithmic units) of the X-ray-to-optical ratio, assuming the X-ray flux of Col. (6) and the derived optical flux upper limits.

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