Fast multi-wavelength variability from a black hole

Correlated fast multiwavelength variability is becoming a key tool forstudying the physics of accretion and ejection of relativistic jets. Usingsimultaneous Xray and nearinfrared data we have recently discovered vibrationsfrom a relativistic jet down to 62.5 ms time scale, which allowed us to estimatethe speed and the size of the jet. We have shown that the properties of thejet depend on the spectral state of the black hole. We will monitor the outburstevolution of a black hole transient with XMM, simultaneously with groundbasedoptical and IR facilities, in order to apply the same technique to differentspectral states. We propose to perform 10 short (7 ksec) XMM observations ofan active black hole, in order to cover the different stages of the outburst. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]