Fast X-ray-IR variability in accreting neutron stars

Fast opticalinfrared photometry applied to black hole transients has shown tobe one of the most powerful tools to probe the jets in its innermost regions.Extending this approach to accreting neutron stars (NS) we discovered duringAO17 the presence in 4U172834 of subsecond correlated variability between theXray and IR emission, arising most probably from a relativistic jet. Moreover,we also detected an IR burst lagging an Xray burst, allowing us to measure theorbital period of the system. These new fascinating results open a new window onthe study of the accretion processes around NS. We ask to perform 6 (total 63ks)XMM pointings to be matched by 6 (total 14h) HAWKI@VLT observations of 4U0614+09 and 4U 172834, 4U 170544 in order to explore the fast variability in NS. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]