In the settling accretion theory , which is applicable to quasi-spherical accreting slowly rotating magnetized neutron stars with X-ray luminosity L _ { x } \lesssim 4 \times 10 ^ { 36 } erg/s , bright X-ray flares ( \sim 10 ^ { 38 } -10 ^ { 40 } ergs ) observed in supergiant fast X-ray transients ( SFXT ) may be produced by sporadic capture of magnetized stellar-wind plasma from the early-type supergiant .
At sufficiently low steady accretion rates ( \lesssim 10 ^ { 15 } g/s ) through the shell around the neutron star magnetosphere at the settling accretion stage , magnetic reconnection can temporarily 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 , R _ { B } ^ { 3 / 2 } / \sqrt { GM } \sim 10 ^ { 3 } -10 ^ { 4 } s ( R _ { B } is the classical Bondi capture radius ) , and the typical energy released in an SFXT bright flare corresponds to the mass of the shell .