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GCN Circular 480

Subject
GRB 991208 Infrared Detection
Date
1999-12-18T00:09:47Z (24 years ago)
From
Josh Bloom at CIT <jsb@astro.caltech.edu>
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/

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