TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3551 SUBJECT: GRB 050525A: Swift Late-Time Decay Rate DATE: 05/06/21 20:27:28 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC GRB 050525A: Swift Late-Time Decay Rate S. T. Holland, (GSFC/USRA), D. Band (GXFC), A. Blustin (MSSL), P. Boyd (GSFC/UMBC), F. Marshall (GSFC), K. Mason (MSSL), M. Perri (ASI), A. Breeveld (MSSL), P. Brown, A. Cucchiara, C. Gronwall, S. Hunsberger, M. Ivanushkina (PSU), W. Landsman (GSFC), K. McGowan (MSSL), A. Morgan (PSU), M. De Pasquale, T. Poole (MSSL), P. Roming (PSU), S. Rosen, (MSSL), P. Schady (MSSL), M. Still (GSFC/USRA), J. Nousek (PSU), N. Gehrels (GSFC), on behalf of the Swift UVOT team report: Swift/UVOT data suggest that there is a jet break at 17,979 s (0.205 d) after the BAT trigger (Band et al. 2005, GCN 3466) in the optical/ultraviolet afterglow of GRB 050525A. The observed decay index after the jet break is -1.73. The Swift/XRT data also show a late-time break followed by a steep power-law decay. If we extrapolate the UVOT late-time decay to the time of the HST F625W observation (Soderberg 2005, GCN 3550) the predicted magnitude of the optical afterglow is approximately V = 27.4. Therefore the HST observations suggest that the optical afterglow of GRB 050525A was approximately three magnitudes brighter at 18 days after the burst than expected from the fireball model alone. More data are needed to determine if this additional luminosity is due to a host galaxy or some form of rebrightening such as a supernova or a dust echo.