TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3368 SUBJECT: GRB 050505: Keck absorption spectrum and redshift (z=4.27) DATE: 05/05/06 08:36:50 GMT FROM: Edo Berger at Carnegie Obs Edo Berger (Carnegie Observatories), S. Bradley Cenko, Chuck Steidel, Naveen Reddy, and Derek B. Fox (Caltech) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: "We obtained a 900-sec spectrum of the optical candidate (GCN 3366) of GRB 050505 (GCN 3360) with LRIS on the Keck I 10-m telescope on 2005, May 6.27 UT. We find very strong absorption over the range of 6200-6500 A, corresponding to Ly alpha absorption around z = 4.1 to 4.3. In addition, we find several metal absorption lines, including SiIV (1393,1402), at a redshift of 4.27. At this redshift, the second highest measured for any GRB, the isotropic equivalent gamma-ray energy is 7.7e53 erg."