GRB 221009A: Redshift from X-shooter/VLT

We observed the afterglow of the extremely bright GRB221009A (Dichiara et al., GCN 32632; Kennea & Williams, GCN 32635; Bissaldi et al., GCN 32637; Veres et al., GCN 32636; Lesage et al., GCN 32642) with X-shooter at ESO's UT3 of the Very Large Telescope (Paranal, Chile). The observations started at 00:49:58.9 UT (11.55 hr after the GBM trigger and 10.66 hr after the BAT trigger). The observation consisted of 4x600s with a spectral coverage between 3000 and 21000 AA. We detect a very red continuum with absorption features that correspond to CaII, CaI and NaID at a redshift of z = 0.151. We also detect multiple features due to the Milky Way's interstellar medium, due to the large Galactic column density of material along this line of sight. At this redshift the event has an isotropic equivalent energy of Eiso=2x10^54 erg (using the GBM fluence reported in GCN 32642), barring saturation effects in the Fermi/GBM fluence. This is within the upper end of GRB energetics. Further follow-up is strongly encouraged. We acknowledge the excellent support provided by the Paranal staff, in particular A. Escorza and Zahed Wahhaj.