Lara Sidoli: Transient outburst mechanisms

Supergiants Fast X-ray Transients (SFXTs) present short transient X-ray emissions (first observed: XTE J1739) associated with OB supergiant companions and have a high dynamical range of luminosity between outbursts and quiescent phases. Different mechanisms are evoked to explain the short outbursts. The most obvious one involved a spherically symmetric clumpy wind from the companion. Observations of IGR J11215 suggested a different mechanism involving an equatorial disk wind from the supergiant. Finally, the third mechanism involves an outburst being driven by a magnetic barrier in which the wind accretion is prevented by a high magnetic field (magnetar-like) and a long spin period. More data are still required and the present monitoring campaign with Swift should address what mechanism is best suited to explain the different behaviors observed among the SFXTs population.