GCN Circular 460
GRB 991208 Keck Spectroscopy A. Diercks, J. S. Bloom, S. G. Djorgovski, L. Hillenbrand, and J. Carpenter (Caltech) report on behalf of the Caltech-NRAO-CARA GRB collaboration: "A 1500-s spectrum of the afterglow of GRB 991208 (GCN #450; GCN #451; GCN #452) was obtained on the night of 14 Dec 1999 UT at the Keck II 10-m Telescope on Mauna Kea by L. Hillenbrand and J. Carpenter (Caltech). The observations were conducted using the Low-Resolution Imaging Spectrometer (LRIS; Oke et al. 1995) with a 400 line/mm grating blazed at ~8500 Ang giving an effective wavelength coverage of ~6250 - 9050 Ang. A previously-measured instrument response function was used for an approximate flux calibration. Interestingly, the spectrum appears very blue, in contrast with theoretical expectations for an afterglow. Though the spectrograph slit was aligned close to the parallactic angle, the observations were performed at an airmass of ~3.6 and with a bright dawn sky foreground. However, we do not think that the observed spectral slope can be entirely explained by the differential slit losses. The extreme blueness is so puzzling that we strongly encourage multiband photometric or additional spectrophotometric observations to check this potentially interesting result. This message may be cited."