092368

Correlated fast multi-wavelength variability is a powerful tool for studying thephysics of accretion and ejection in X-ray binaries. Using simultaneous X-rayand near-IR data we have secured the first detection of sub-second IRvariability from a jet (including quasi-periodic oscillations) in a BH LMXBallowing us to estimate the jet speed and size. Further data showed thatsignificant jet variability is also present in NS LMXBs opening a new window inthe study of jets. Here we propose to monitor the evolution of an outburst ofboth systems with XMM simultaneously with ground-based optical infraredfacilities across different spectral states. Thus we propose to perform up to20 short XMM observations (7 ks each) to cover the different stages of the outburst in both systems. [truncated! Please see actual data for full text]