  INTEGRAL, the European Space Agency's gamma-ray observatory, tripled the
number of super-giant high-mass X-ray binaries (sgHMXB) known in the Galaxy by
revealing absorbed and fast transient (SFXT) systems. In these sources,
quantitative constraints on the wind clumping of the massive stars could be
obtained from the study of the hard X-ray variability of the compact accreting
object. Hard X-ray flares and quiescent emission of SFXT systems have been
characterized and used to derive wind clump parameters. A large fraction of the
hard X-ray emission is emitted in the form of flares with a typical duration of
3 ks, frequency of 7 days and luminosity of 1E36 erg/s. Such flares are most
probably emitted by the interaction of a compact object orbiting at ~10 R* with
wind clumps (1E(22-23) g) representing a large fraction of the stellar
mass-loss rate. The density ratio between the clumps and the inter-clump medium
is 1E(2-4) in SFXT systems. The parameters of the clumps and of the inter-clump
medium, derived from the SFXT flaring behavior, are in good agreement with
macro-clumping scenario and line driven instability simulations. SFXT have
probably a larger orbital radius than classical sgHMXB.
