1120014

The mass transfer and accretion mechanisms in SFXTs are key questions to be answered in order to place the SFXTs in the wider context of HMXB systems. Current theories centre on mass transfer via isotropic but inhomogeneous (clumpy) winds but some systems also show evidence of disk-like structures around the supergiant analogous to those seen in Be/X-ray binaries. We propose a campaign of periastron observations of 2 SFXTs with known ephemerides following on from accepted and successful AO-9 and AO-10 programmes (P.I. Drave PropIDs 0920016 and 1020009). Using both INTEGRAL and XMM-Newton we will measure the instantaneous accretion rate emission spectrum and time variability generated on and around the neutron star during its periastron passage. Now that the orbital parameters of these SFXTs are well-determined targeted continuous broad-band observations around periastron provide us with the best opportunity to use the (assumed) neutron star as a direct probe of the circumstellar wind environment. To achieve the goals outlined in this proposal we request 630 ks of fixed time INTEGRAL observations complemented with 100 ks of simultaneous XMM-Newton observations. [truncated! Please see actual data for full text]