Probing the nature of the circumstellar environment during periastron passage

The mass transfer and accretion mechanisms in SFXTs are key questions to placethem in the wider context of HMXB systems. Current theories centre on masstransfer via isotropic but inhomogeneous (a??clumpya??) winds, but some systemsalso show evidence of disklike structures around the supergiant, analogous tothose seen in Be/Xray binaries. We propose a campaign of periastronobservations of 2 SFXTs with known ephemerides. Simultaneous INTEGRAL/XMMobservations will measure the instantaneous accretion rate, emission spectrumand time variability generated on and around the neutron star. Continuousbroadband observations around periastron yield the best opportunity to use theneutron star as a direct probe of the circumstellar wind environment. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]