TITLE: GCN CIRCULAR NUMBER: 20584 SUBJECT: GRB 170202A: Redshift from OSIRIS/GTC DATE: 17/02/03 00:22:15 GMT FROM: Antonio de Ugarte Postigo at IAA-CSIC A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), L. Izzo (IAA-CSIC), C. Thoene (IAA-CSIC), D.A. Kann (IAA-CSIC, TLS), P. Pessev (GRANTECAN, IAC, ULL), A. Perez (GRANTECAN) report on behalf of a larger collaboration: We observed the afterglow of GRB 170202A (Racusin et al. GCN 20575) using OSIRIS at the 10.4m GTC telescope at the Roque de los Muchachos observatory (La Palma, Spain). The observation started at 23:22 UT (4.91 hr after the burst) and included observations with grisms R1000B and R1000R covering the ranges 3700 - 7800 AA and 5100 - 9300 AA respectively. The blue spectra shows a strong signal with multiple features being especially significant Lyman-alpha (both in absorption and emission), the full Ly-forest, NV, SII, SiII, SiII*, OI, CII, SiIV, CIV and AlII at a common redshift of 3.645, which we identify as the redshift of the GRB.