TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1635 SUBJECT: GRB 021004: optical spectroscopy on Oct 11 DATE: 02/10/14 19:12:38 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia A. J. Castro-Tirado, E. Pérez, J. Gorosabel (IAA-CSIC, Granada), J. M. Castro Cerón (ROA, San Fernando), M. Andersen (AIP, Potsdam), J. Hjorth (Univ. of Copenhagen), E. Rol, R. Wijers (Univ. of Amsterdam), A. Fruchter (STScI, Baltimore), S. Klose (TLS, Tautenburg), J. Greiner (MPE, Garching) and E. Pian (OAT-INAF, Trieste) on behalf of the GRACE Collaboration report: "We have obtained a 7200-s spectrum with the FORS1 spectrograph at the ESO's 8.2-m VLT3 telescope at Paranal on Oct 11.125-11.231 UT. The range is 3500- 5700 A with a resolution of about 1 A/pix. We confirm the detection of the Ly-alpha (1215.7 A) emission line plus the C IV (1548,2 A, 1550.8 A) absorption line system at a redshift z = 2.327 (GCN 1605). The Al II (1670 A) absorption line (GCN 1618) is detected as well at the same redshift. We also detect another two absorption line systems at z = 2.297 and z = 2.321 on the basis of C IV (1548,2 A, 1550.8 A) lines. The latter system is also detected in Si IV (1393.8, 1402.8). These two systems are consistent with those reported by Salamanca et al. (GCN 1611) and Savaglio et al. (GCN 1633). The flux of the Ly-alpha line (1.9e-16 erg/cm2/s/A) is comparable with the one measured by Keck (GCN 1620), i.e. the Lyman-alpha flux is constant and we conclude that arises from the GRB 021004 host galaxy, at z = 2.327." This message may be cited.