TITLE: GCN GRB OBSERVATION REPORT NUMBER: 481 SUBJECT: GRB 991208 Keck Spectroscopy DATE: 99/12/18 01:25:49 GMT FROM: George Djorgovski at Caltech/Palomar GRB 991208 Keck Spectroscopy S. G. Djorgovski, A. Dierks, J. S. Bloom, S. R. Kulkarni (Caltech), A. V. Filippenko (UC Berkeley), L. A. Hillenbrand, and J. Carpenter (Caltech), report on behalf of the Caltech-CARA-NRAO GRB collaboration: We recalibrated and combined the Keck spectra of GRB 991208 obtained on 14 and 15 Dec 1999 UT, for which preliminary results were reported earlier (GCN #460, GCN #464). Addition of the spectra improved the total S/N as expected. We confirm the existence of emission lines at the observed wavelengths 6356, 8454, and 8545 Ang, reported by Dodonov et al. (GCN #475). We agree with their proposed identifications as [O II] 3727, and [O III] 4959, 5007, giving the redshift z = 0.7055 +- 0.0005. However, we note that the proximity of the strong night sky lines (especially for the tentative 8454 Ang line), and additional spectroscopic observations are still needed in order to firm up this result. Assuming z = 0.7055, and the standard Friedmann cosmology with h = 0.65, Omega_0 = 0.2, and Lambda_0 = 0, the luminosity distance is 1.30E28 cm. Assuming the integrated gamma-ray fluence of >~ 1.E-4 erg/cm2 (GCN #450), the implied isotropic energy is ~ 1.3E53 erg, which of course may be affected by beaming. We also performed a power-law fit to the fully calibrated and extinction corrected spectrum from UT Dec. 15.64. For F_nu ~ nu ** beta, we obtain beta = -0.9 +- 0.15, in a good agreement with the photometric measurement reported by Bloom et al. (GCN #480). This message may be cited.