  Results: The two Wolf-Rayet stars WR20a (WN6ha+WN6ha) and WR20b (WN6ha) were
analyzed in detail. They are both very luminous and display very hard spectra,
but WR20b does not seem to vary. On the contrary, WR20a, a known eclipsing,
colliding-wind binary, brightens in the X-ray domain during the eclipses, i.e.
when the collision is seen face-on. This can be explained by the properties of
the wind-wind collision zone, whose high density leads to a large absorbing
column (2 10^24 cm^-2).All twelve O-type stars previously classified
spectroscopically, two eclipsing binaries previously identified and nine newly
identified O-type star candidates are detected in the high energy domain; ten
of them could be analyzed spectroscopically. Four are overluminous, but the
others present typical L_X/L_BOL ratios, suggesting that several O-type objects
are actually binaries. Variability at the ~2sigma level was detected for a
majority of the sources, of unknown origin for the putatively single objects.
Faint, soft, diffuse emission pervades the entire field-of-view but no clear
structure can be identified, even at the position of a blister proposed to be
at the origin of the TeV source HESS J1023-575. Finally, the X-ray properties
of PMS objects were also investigated, in particular the brightest flaring
ones. They provided an additional argument in favor of a large distance (~8kpc)
for the cluster.
