Supergiant Fast X-ray Transients: a review
  Supergiant Fast X-ray Transients are a class of Galactic High Mass X-ray
Binaries with supergiant companions. Their extreme transient X-ray flaring
activity was unveiled thanks to INTEGRAL/IBIS observations. The SFXTs dynamic
range, with X-ray luminosities from 1E32 erg/s to 1E37 erg/s, and long time
intervals of low X-ray emission, are puzzling, given that both their donor star
properties and their orbital and spin periodicities seem very similar to those
displayed by massive binaries with persistent X-ray emission. Clumpy supergiant
winds, accretion barriers, orbital geometries and wind anisotropies are often
invoked to explain their behavior, but still several open issues remain. A
review of the main recent observational results will be outlined, together with
a summary of the new scenarios proposed to explain their bright flaring X-ray
activity. The main result of a long Suzaku observation of the SFXT
IGRJ16479-4514 with the shortest orbital period is also briefly summarized. The
observation of the X-ray eclipse in this source allowed us to directly probe
the supergiant wind density at the orbital separation, leading to the
conclusion that it is too large to justify the low X-ray luminosity. A
mechanism reducing the accretion rate onto the compact object is required.
