Bloom, J. S.Berger, E.Kulkarni, S. R.Djorgovski, S. G.Frail, D. A.2019-09-272003Bloom, J. S., E. Berger, S. R. Kulkarni, S. G. Djorgovski, and D. A. Frail. 2003. “The Redshift Determination of GRB 990506 and GRB 000418 with the Echellete Spectrograph Imager on Keck.” The Astronomical Journal 125 (3): 999–1005. https://doi.org/10.1086/367805.0004-62561538-3881http://nrs.harvard.edu/urn-3:HUL.InstRepos:41417342Using the Echellete Spectrograph Imager (ESI) on the Keck II 10 m telescope we have measured the redshifts of the host galaxies of gamma-ray bursts GRB 990506 and GRB 000418, z = 1.30658 +/- 0.00004 and 1.1181 +/- 0.0001, respectively. Thanks to the excellent spectral resolution of ESI (lambda/Deltalambda = 13000), we resolved the [O II] lambda727 doublet in both cases. The measured redshift of GRB 990506 is the highest known for a dark-burst GRB, though entirely consistent with the notion that dark and non-dark bursts have a common progenitor origin. The relative strengths of the [O II], He I [Ne III], and Hgamma emission lines suggest that the host of GRB 000418 is a starburst galaxy, rather than a LINER or Seyfert 2. Since the host of GRB 000418 has been detected at submillimeter wavelengths, these spectroscopic observations suggest that the submillimeter emission is due to star formation ( as opposed to AGN) activity. The [O II]-derived unobscured star formation rates are 13 and 55 M(circle dot) yr(-1) for the hosts of GRB 990506 and GRB 000418, respectively. In contrast, the star formation rate of the host of GRB 000418 derived from submillimeter observations is 20 times larger.en-USJournal Article2019-09-2710.1086/367805