TITLE: GCN CIRCULAR NUMBER: 7991 SUBJECT: GRB 080721: Swift/UVOT Photometric Redshift DATE: 08/07/21 15:05:46 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland, P. A. Ward (MSSL-UCL), and F. E. Marshall (NASA/GSFC) report on behalf of the Swift/UVOT Team: Preliminary UVOT photometry of the afterglow of GRB 080721 (Marshall, et al. 2008, GCN Circ. 7988) shows that the afterglow is strongly detected in the U band, but not in the UVW1, UVM2, or UVW2 bands at approximately 825 s after the BAT trigger. This suggests that the redshift of GRB 080721 may be greater than approximately 2.3.