TITLE: GCN GRB OBSERVATION REPORT NUMBER: 251 SUBJECT: GRB 990123: Updated Keck Spectroscopy Results DATE: 99/02/05 02:31:18 GMT FROM: George Djorgovski at Caltech/Palomar GRB 990123: Updated Keck Spectroscopy Results S. G. Djorgovski, S. R. Kulkarni (CIT), G. D. Illingworth (UCSC), D. D. Kelson (DTM), J. S. Bloom, S. C. Odewahn, R. R. Gal (CIT), M. Franx (Leiden), P. van Dokkum (Groningen), D. Magee (UCSC), and D. A. Frail (NRAO) note on behalf of the Caltech-UC-CARA-NRAO collaboration: Our re-reduction of the Keck spectrum of the optical transient associated with GRB 990123 (Kelson et al., IAUC 7096) gives the following results: We detect 12 (13) absorption lines in the spectrum of the OT, as follows: W_obs,air W_rest,vac z Line ID 4843.74 1862.78 1.6010 Al III 5267.29 2026.14 1.6004 Zn II 5361.77 2062.23 1.6007 Cr II | blend 5361.77 2062.66 1.6002 Zn II | 5877.17 2260.78 1.6003 Fe II 6096.14 2344.21 1.6012 Fe II 6173.87 2373.73 1.6016 Fe II 6195.29 2382.76 1.6008 Fe II 6725.75 2586.64 1.6009 Fe II 6759.94 2600.18 1.6005 Fe II 7269.47 2796.35 1.6003 Mg II 7289.49 2803.53 1.6008 Mg II 7416.97 2852.97 1.6005 Mg I The mean redshift is 1.6004 +- 0.0005 (random) +- 0.0005 (systematic). This agrees to within the quoted error with the new determination of the absorber redshift by Hjorth et al. (GCN 249). We note the remarkably small velocity dispersion implied by these data, less than about 60 km/s in the restframe, suggesting that the lines arise from a single subgalactic-size cloud (which of course may be a part of the host galaxy's ISM), rather than from an ansamble of clouds moving within the potential well of a normal, massive galaxy. It is also possible that the GRB host is a dwarf galaxy, in which case the object detected near the line of sight both in the K band (Djorgovski et al., GCN 243) and in the R band (Yadigaroglu and Halpern, GCN 248) may be a foreground galaxy. No other convincing absorption systems, and no emission lines are detected in these data, in the useful wavelength range of approximately 4700 to 9000 Angstroms. We do not detect Ca II H+K absorption, nor any other common absorption lines, e.g., Na D, nor any common emission lines (e.g., [O II] 3727, H alpha, H beta, etc.) from either of the two absorption systems originally proposed by Hjorth et al. (GCN 219). We have also measured the redshift of the galaxy approximately 10 arcsec west of the OT. From 4 relatively "clean" lines, Ca II H+K, H beta, and H alpha, we derive for its redshift z = 0.2783 +- 0.0005. From 4 blended lines, CH G-band 4300, Mg I 5173+5184, Fe I + Ca I 5267, and Na D 5893, we derive z = 0.278 +- 0.001, again in an excellent agreement with Hjorth et al. (GCN 249). No absorption or emission lines corresponding to this redshift are seen in the spectrum of the OT. This report may be cited.