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GCN Circular 460

Subject
GRB 991208 Keck Spectroscopy
Date
1999-12-15T06:37:17Z (24 years ago)
From
Josh Bloom at CIT <jsb@astro.caltech.edu>
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."
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