GCN Circular 8303
Alejandro Ferrero (UCD School of Physics), John French (UCD School of Physics/ DARK/NBI), and Gary Melady (UCD School of Physics) report on behalf of a larger collaboration: We observed the field of GRB 080928� (Sakamoto et al. GCN 8292) with the Watcher robotic telescope at Boyden Observatory, South Africa. The afterglow previously reported (Sakamoto et al. GCN 8292, Rykoff et al. GCN 8293, Rossi et al. GCN 8296, Kuin et al. GCN 8298) is detected in a stacked sequence of 10 unfiltered 120s exposures with an exposure midtime of 10.56 hrs from the Swift triggger. Comparison with USNO-B1 R-band magnitudes gives a magnitude of 19.37 +/- 0.11 for the optical afterglow at this time. Comparison with later GROND observations (Rossi et al. GCN 8296) indicates a steep decay slope of approx. -3 +/- 0.4 from 10.56 hours to 18.27 hours from the trigger.