[vsnet-grb-info 1710] GRB 050525A: Swift Late-Time Decay Rate

[GCN Circulars]

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  <sholland at milkyway.gsfc.nasa.gov>

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.