GCN Circular 3932
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." This message may be cited.