[vsnet-grb-info 2538] GRB 051221: Discovery of fading optical afterglow

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4375
SUBJECT: GRB 051221: Discovery of fading optical afterglow
DATE:    05/12/21 19:04:50 GMT
FROM:    Alicia Soderberg at Caltech  <ams at astro.caltech.edu>

A. M. Soderberg (Caltech) and E. Berger (Carnegie Observatories) report:

"Digital image subtraction performed on the individual 240-s r-band frames
obtained with Gemini/GMOS (GCN 4369) reveal a fading source coincident
with the position of the bright NIR (GCN 4367) and optical (GCN 4369)
object located within the XRT error circle (GCN 4366).  The fading source
is offset from the center of the bright object, which we identify as the
host galaxy, by about 0.2" to the west.  Given the offset and fading
behavior we conclude that this object is the afterglow of GRB 051221.
Detailed photometry is in progress."