  At steady low-luminosity states, Supergiant Fast X-ray Transients (SFXTs) can
be at the stage of quasi-spherical settling accretion onto slowly rotating
magnetized NS from the OB-companion winds. At this stage, a hot quasi-static
shell is formed above the magnetosphere, the plasma entry rate into
magnetosphere is controlled by (inefficient) radiative plasma cooling, and the
accretion rate onto the NS is suppressed by a factor of \sim 30 relative to the
Bondi-Hoyle-Littleton value. Changes in the local wind velocity and density can
only slightly increase the mass accretion rate (a factor of \sim 10) bringing
the system into the Compton cooling dominated regime and led to the production
of moderately bright flares (L_x\lesssim 10^{36} erg/s). To interpret the
brightest flares (L_x>10^{36}~erg/s) displayed by the SFXTs, we propose that a
larger increase in the mass accretion rate can be produced by sporadic capture
of magnetized stellar wind plasma. At sufficiently low accretion rates,
magnetic reconnection can enhance the magnetospheric plasma entry rate,
resulting in copious production of X-ray photons, strong Compton cooling and
ultimately in unstable accretion of the entire shell. A bright flare develops
on the free-fall time scale in the shell, and the typical energy released in an
SFXT bright flare corresponds to the mass of the shell. This view is consistent
with the energy released in SFXT bright flares (\sim 10^{38}-10^{40}~ergs),
their typical dynamic range (\sim 100), and with the observed dependence of
these characteristics on the average unflaring X-ray luminosity of SFXTs. Thus
the flaring behavior of SFXTs, as opposed to steady HMXBs, may be primarily
related to their low X-ray luminosity allowing sporadic magnetic reconnection
to occur during magnetized plasma entry into the magnetosphere.
