TITLE: GCN GRB OBSERVATION REPORT NUMBER: 480 SUBJECT: GRB 991208 Infrared Detection DATE: 99/12/18 00:09:47 GMT FROM: Josh Bloom at CIT GRB 991208 Infrared Detection J. S. Bloom, A. Diercks, S. R. Kulkarni, S. G. Djorgovski, N. Z. Scoville, D. T. Frayer (Caltech) report on behalf of the Caltech-NRAO-CARA GRB Collaboration: "On 16 December 1999 UT N. Scoville and D. Frayer observed the field of GRB 991208 with the slit-viewing camera of the Near-Infrared Echelle Spectrograph (NIRSPEC; McLean et al. SPIE, 1998) at the Keck II 10-m Telescope on Mauna Kea, Hawaii. In a stacked 1560-s imaging exposure we detect a K-band source at the position of the transient afterglow (GCN #450, GCN #451, GCN #452) of GRB 991208. We find no clear extension of this presumed IR afterglow with respect to other stars in the field. We note the presence of a faint extended galaxy ~8.3" W of the source. Comparison with standard star SJ 9162 (Persson, AJ, 1998) yields a preliminary magnitude of the afterglow of K=19.31 +/- 0.15 mag (16.68 Dec 1999 UT). Extrapolating the R-band light curve using the reported decay slope from Masetti et al. (GCN #462), on 16.68 Dec 1999, we find R - K = 2.7 (including the small Galactic extinction) implying a spectral index beta = -0.77 +/- 0.14 (statistical uncertainty). We note this optical-IR spectral index is inconsistent with reports of an apparent blue spectrum from preliminary reductions of optical spectroscopy (GCN #460, GCN #461)." A K-band finding chart can be found at http://astro.caltech.edu/~jsb/GRB/grb991208/ This message may be cited.