TITLE: GCN GRB OBSERVATION REPORT NUMBER: 497 SUBJECT: GRB 991216 Optical spectroscopy/imaging DATE: 99/12/19 06:25:27 GMT FROM: Alan H. Diercks at Caltech GRB 991216 Optical spectroscopy/imaging A. Diercks, J. S. Bloom, S. G. Djorgovski, S. R. Kulkarni, B. T. Soifer, D. J. Thompson, R. R. Gal, and A. Mahabal report on behalf of the Caltech-NRAO-CARA GRB group: Spectra of the OT associated with GRB 991216 were obtained at the WMKO Keck-II 10-m telescope by B. T. Soifer and D. J. Thompson on Dec. 18.3 UT, using LRIS instrument (Oke et al. 1995). Grating with 150 l/mm was used, giving the useful coverage of ~ 5600 - 10400 Ang, with a mean dispersion of ~ 4.86 Ang/pixel. Despite a strong continuum detection, no significant absorption or emission features (other than atmospheric) have been detected in the summed spectrum. Absorbers at z ~< 1, as reported by Vreeswijk et al. (GCN #496), would be outside the wavelength range of our data. In addition, we measure R = 20.30 +/- 0.06 at Dec 18.40 UT from 5 150s imaging exposures with LRIS. The OT was calibrated against star "B" (Jha et al. GCN #476) with R=19.45 (Dolan et. al., GCN #486). The images were taken in 0.75" seeing and the pixel scale is 0.21 arc-seconds/pixel. At this resolution, the PSF of the OT is consistent that with neighboring stars, and we find no evidence for the excess 'fuzziness' reported by Schaefer (GCN #485). No host galaxy is detected on the Digital POSS-II (DPOSS) scans, corresponding to approximate limits of g > 21, r > 20.5, and i > 20 mag (conservative limits) in the Gunn system. This is consistent with the absence of flattening of the light curve so far, and the lack of detectable extension or PSF residuals in our Keck LRIS images.