TITLE: GCN CIRCULAR NUMBER: 15922 SUBJECT: GRB 140304A: 10.4m GTC redshift z = 5.39 DATE: 14/03/04 22:01:48 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia S. Jeong, R. Sánchez-Ramírez (IAA-CSIC), A. J. Castro-Tirado (IAA-CSIC, UMA), J. Gorosabel (EHU-UPV, IAA-CSIC), M. Jelinek, J. C. Tello, P. Ferrero, O. Lara-Gil, R. Cunniffe (IAA-CSIC), D. Pérez-Ramírez (U. Jaén), S. Guziy (Nikolaev Univ.), J. M. Castro Cerón (ESAC), A. Fernández-Soto (UV), J. Cepa (IAC), M. A. Rivero and G. Gómez-Velarde (GTC), on behalf of a larger collaboration, report: “Following the detection of the optical afterglow (Gorbovskoy et al. GCNC 15914) to GRB 140304A (Evans et al. GCNC 15915), we have obtained an optical spectrum with the 10.4 m GTC (+OSIRIS) starting aprox. 8.2 hr postburst, covering the 5700-10000 wavelength range. The continuum is detected only redwards of aprox. 7750 A, with several absorption metallic lines (N V, Si II and Si IV amongst others) at a common redshift of z = 5.39 which we propose to be the redshift of GRB 140304A. This is consistent with the Swift/UVOT upper limits (Marshall et al. GCNC 15920) and the NOT optical observation (de Ugarte Postigo et al. GCNC 15921).” [GCN OPS NOTE(04mar14): Per author's request, the "5.XX" was replaced with 5.39.]