GCN Circular 20078
P. D'Avanzo (INAF-OAB), D. Malesani (DARK/NBI and DTU Space), V. D'Elia (INAF/OAR & ASI/ASDC), A. Melandri (INAF-OAB), V. Lorenzi, H. Stoev (INAF-TNG) report on behalf of the CIBO collaboration: We observed the optical afterglow of GRB 161017A (Yurkov et al. GCN 20063; Troja et al. GCN 20064; de Ugarte Postigo et al. GCN 20069; Fujiwara et al. GCN 20070; Guidorzi et al. GCN 20072; Breeveld & Troja, GCN 20074; Sadovnichy et al. GCN 20075) with the 3.6m Telescopio Nazionale Galileo (TNG) equipped with the DOLoRes camera in spectroscopic mode. Observations were carried out with the LR-B filter, covering the range 3500-8000 AA. The observations consisted of two spectra, each one lasting 1200 s, carried out at a mean time of Oct 18.1852 UT (~10.58 hours after the burst). The spectrum shows a clear continuum. We detect absorption features consistent with Li-alpha, Si II, C IV and Fe II lines at a common redshift of z = 2.01, together with MgII intervening systems at z=0.92 and z=1.37, in agreement with the results reported by de Ugarte Postigo et al. (GCN 20069) and Castro-Tirado et al. (GCN 20077).