TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3520
SUBJECT: GRB 050603: Redshift 
DATE:    05/06/05 21:52:43 GMT
FROM:    Edo Berger at Carnegie Obs  <eberger@ociw.edu>

Edo Berger (Carnegie Observatories) and George Becker (Caltech) report:

"We obtained a 45-min spectrum of the afterglow of GRB 050603 (GCNs 3509,
3511) with IMACS on the Magellan/Baade telescope on 2005, June 5.40 UT
(2.13 days after the burst).  We find a single bright emission line at an
observed wavelength of 4645.1A, which we interpret as Lyman-alpha at a
redshift of z=2.821.

At this redshift the isotropic-equivalent gamma-ray energy is 2.3e54 erg
(using a fluence of 3.4e-5 erg/cm^2; GCN 3518).  The steep fading observed
by the UVOT (GCN 3517) and XRT (GCN 3519) suggests a jet break at t~12
hours after the burst, corresponding to a jet opening angle of about 1.7
deg, and hence a beaming-corrected energy of 1.1e51 erg."