TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3932
SUBJECT: GRB 050904: Keck I-band Imaging
DATE:    05/09/06 18:58:03 GMT
FROM:    Josh Bloom at UC Berleley  <jbloom@astron.berkeley.edu>

D. Perley, J. S. Bloom, M. Cooper (UCB), J. Newman (LBL), P.  
Guhatakurta (UCSC), J. X. Prochaska (UCO Lick) and H.-W. Chen (MIT/U  
Chicago) report on behalf of a larger group:

"We observed the field of GRB 050904 (GCN 3910) using the DEIMOS  
imager on the Keck II during the early morning twilight of 05 Sept  
2005 UT.  The afterglow candidate reported by Haislip et al. (GCN  
3913, 3922) is well-detected in the first 300-second I-band exposure,  
taken at UTC=14:50 (~37.0 hours after the burst).  Calibrating  
against three nearby stars in SDSS, we measure a preliminary  
magnitude for the afterglow of i~=22.9 +/- 0.6. This uncertainty is  
dominated by the photometric calibration which we expect to improve  
with further processing."

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