  Supergiant Fast X-ray Transients (SFXTs) are a sub-class of High Mass X-ray
Binaries (HMXBs) associated with OB supergiant companions and displaying
transient X-ray activity. This behaviour is quite surprising since HMXBs
hosting supergiants were known to be persistent sources, until the INTEGRAL
discoveries obtained by means of the monitoring of the Galactic plane. We have
been performing a monitoring campaign with Swift of four SFXTs with the main
aim of characterizing both the long-term behaviour of these transients and the
properties during bright outbursts. Here we discuss the properties of the X-ray
emission observed outside the outbursts as well as the flares observed from two
SFXTs: IGRJ17544-2916 and XTEJ1739-302. Contrarily to what previously thought,
Swift allowed us to discover that SFXTs spend most of the time in accretion at
a low level, even outside the bright outbursts, with an accretion luminosity of
1E33-1E34 erg/s, and that the quiescent level at ~1E32 erg/s is a much rarer
state.
