GCN Circular 497
Subject
GRB 991216 Optical spectroscopy/imaging
Date
1999-12-19T06:25:27Z (25 years ago)
From
Alan H. Diercks at Caltech <ad@astro.caltech.edu>
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.