TITLE: GCN CIRCULAR NUMBER: 20104 SUBJECT: GRB 161023A VLT/X-shooter redshift DATE: 16/10/24 03:17:06 GMT FROM: Nial Tanvir at U.Leicester N. R. Tanvir (U. Leicester), T. Kruehler (MPE), A. De Cia (ESO), K. Wiersema (U. Leicester), D. Xu (NAOC), D. Malesani (DARK/NBI), report on behalf of a larger collaboration: We observed the optical counterpart of the bright INTEGRAL GRB 161023A (Mereghetti et al. GCN 20103; Gorbovskoy et al. GCN 20102) with the ESO Very Large Telescope UT 2 (Kueyen) equipped with the X-shooter spectrograph, covering the wavelength range 3500-20000 AA. Observations started on October 24.05 UT (approx 3.0 hr after the GRB) and consisted of 2 exposures of 600 s each. The spectrum exhibits numerous absorption features including the hydrogen Lyman series, and lines of SII, SiII, SiIV, CIV, AlII, FeII, OI, several of which are fine structure lines, at a redshift of z=2.708. We conclude this is the redshift of the GRB. We acknowledge the generosity of the visiting observer, Chris D'Andrea, who approved the override, and expert support from the ESO observing staff, particularly Linda Schmidtobreick and Luca Sbordone, in obtaining these observations. [GCN OPS NOTE(24oct16): L.Sbordone was added to the last paragraph.]