086421

Fast optical-infrared photometry applied to black hole transients has shown to be one of the most powerful tools to probe the jets in its innermost regions. Extending this approach to accreting neutron stars (NS) we discovered during AO17 the presence in 4U1728-34 of subsecond correlated variability between the X-ray and IR emission arising most probably from a relativistic jet. Moreover we also detected an IR burst lagging an X-ray burst allowing us to measure the orbital period of the system. These new fascinating results open a new window on the study of the accretion processes around NS. We ask to perform 6 (total 63ks) XMM pointings to be matched by 6 (total 14h) HAWK-I@VLT observations of 4U 0614+09 and 4U 1728-34 4U 1705-44 in order to explore the fast variability in NS. [truncated! Please see actual data for full text]