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GCN Circular 481

Subject
GRB 991208 Keck Spectroscopy
Date
1999-12-18T01:25:49Z (24 years ago)
From
George Djorgovski at Caltech/Palomar <george@oracle.caltech.edu>
GRB 991208 Keck Spectroscopy

S. G. Djorgovski, A. Dierks, J. S. Bloom, S. R. Kulkarni (Caltech),
A. V. Filippenko (UC Berkeley), L. A. Hillenbrand, and J. Carpenter 
(Caltech), report on behalf of the Caltech-CARA-NRAO GRB collaboration:

We recalibrated and combined the Keck spectra of GRB 991208 obtained on
14 and 15 Dec 1999 UT, for which preliminary results were reported earlier 
(GCN #460, GCN #464).  Addition of the spectra improved the total S/N as
expected.  We confirm the existence of emission lines at the observed 
wavelengths 6356, 8454, and 8545 Ang, reported by Dodonov et al. (GCN #475).  
We agree with their proposed identifications as [O II] 3727, and [O III] 
4959, 5007, giving the redshift z = 0.7055 +- 0.0005.  However, we note 
that the proximity of the strong night sky lines (especially for the 
tentative 8454 Ang line), and additional spectroscopic observations are 
still needed in order to firm up this result.

Assuming z = 0.7055, and the standard Friedmann cosmology with h = 0.65,
Omega_0 = 0.2, and Lambda_0 = 0, the luminosity distance is 1.30E28 cm.
Assuming the integrated gamma-ray fluence of >~ 1.E-4 erg/cm2 (GCN #450), 
the implied isotropic energy is ~ 1.3E53 erg, which of course may be
affected by beaming.

We also performed a power-law fit to the fully calibrated and extinction
corrected spectrum from UT Dec. 15.64.  For F_nu ~ nu ** beta, we obtain 
beta = -0.9 +- 0.15, in a good agreement with the photometric measurement 
reported by Bloom et al. (GCN #480).

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