TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3709
SUBJECT: GRB 050730: Redshift Measurement based on Magellan/MIKE Observations
DATE:    05/07/31 01:42:59 GMT
FROM:    Hsiao-Wen Chen at MIT/CSR  <hchen@space.mit.edu>

Hsiao-Wen Chen (MIT), Ian Thompson (Carnegie Observatory), Jason X. 
Prochaska (UCO/Lick Observatory), Josh Bloom (UCB) report on behalf of the 
GRAASP collaboration:

"We observed the afterglow of GRB050730 reported by Holland et al. (GCN 3704) 
and Sota et al. (GCN 3705) using the MIKE echelle spectrograph on Magellan II.
The observations started at UT 00:00:04 on July 31, 2005, ~ 4 hours after
the inital Swift/BAT trigger (GCN 3704).  We obtained a high signal-to-noise
(S/N ~ 20 at 8000 Ang) spectrum with a resolution element of ~10 km/s.  We
measure the afterglow at redshift z=3.967 based on a broad absorption trough  
at 6040 Ang, which we identify as the Lya absorption line originated in the 
host of the GRB.  We also detect a suite of strong absorption lines, which we 
confirm as OI1302, SiII 1304, and CII 1334 at this redshift.    

Further analysis is underway.

This message may be cited."