092125

We propose a high-resolution spectral study of the transient black hole X-raybinary MAXI J1810-222 to clearly resolve and determine the nature of one of themost powerful and fastest wind ever observed in a Galactic accreting system. Werequest a 60 ks XMM-Newton observation when the source is either in soft orintermediate state to constrain the physical parameters of the wind with muchgreater accuracy than those derived from the available NICER spectra. Byanalysing these spectra we obtained evidence for a spectral-state dependentoutflow with mildly relativistic speed which would test current theoreticalmodels of winds formation in X-ray binaries. RGS is the only instrument able toresolve sharp features around 1 keV within our observing constraints. [truncated! Please see actual data for full text]