TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  661
SUBJECT: The redshift of GRB 000418
DATE:    00/05/03 06:25:31 GMT
FROM:    Josh Bloom at CIT  <jsb@astro.caltech.edu>

The redshift of GRB 000418

J. S. Bloom, A. Diercks, S. G. Djorgovski, D. Kaplan, and S. R. Kulkarni
(Caltech) report on behalf of the larger Caltech-NRAO-CARA GRB
collaboration:

"We observed the transient position of GRB 000418 (Klose et al. GCN #645)
with the Echellette Spectrograph and Imager (ESI) on the Keck II 10-m
Telescope on Mauna Kea at 2.318 May 2000 UT.  In a 1200-s exposure we
detect both broadband continuum and a strong doublet in emission at
wavelengths Lambda = 7894.0,7899.4 Angstrom (preliminary reduction).  
Further observations of the source are in progress.

We attribute this doublet to [OII] emission from the underlying host
galaxy.  If so, this would place GRB 000418 at a redshift of 
z=1.11854 +/- 0.0007, placing it near the median of GRB redshifts thus far
obtained. Assuming a flat lambda cosmology of H_0 = 65 km/s/Mpc, Omega_m =
0.3, Omega_lam = 0.7 the luminosity distance to the GRB is 
D_L = 2.515 x 10^28 cm.  Since the total fluence of the burst is 
1.3 x 10^{-5} erg cm^{-2} (Hurley et al. GCN #642), we estimate the total
isotropic energy release of the GRB to be E = 4.9 x 10^52 erg."

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