Supergiant Fast X-ray Transients ( SFXT ) are a class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars , and whose X-ray outbursts are about 4 orders of magnitude brighter than the quiescent state .
LOFT , the Large Observatory For X-ray Timing , with its coded mask Wide Field Monitor ( WFM ) and its 10 m ^ { 2 } class collimated X-ray Large Area Detector ( LAD ) , will be able to dramatically deepen the knowledge of this class of sources .
It will provide simultaneous high S/N broad-band and time-resolved spectroscopy in several intensity states , and long term monitoring that will yield new determinations of orbital periods , as well as spin periods .
We show the results of an extensive set of simulations performed using previous observational results on these sources obtained with Swift and XMM-Newton .
The WFM will detect all SFXT flares within its field of view down to a 15–20 mCrab in 5 ks .
Our simulations describe the outbursts at several intensities ( F _ { ( 2 - 10 keV ) } = 5.9 \times 10 ^ { -9 } to 5.5 \times 10 ^ { -10 } erg cm ^ { -2 } s ^ { -1 } ) , the intermediate and most common state ( 10 ^ { -11 } erg cm ^ { -2 } s ^ { -1 } ) , and the low state ( 1.2 \times 10 ^ { -12 } to 5 \times 10 ^ { -13 } erg cm ^ { -2 } s ^ { -1 } ) .
We also considered large variations of N _ { H } and the presence of emission lines , as observed by Swift and XMM–Newton .