TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1339
SUBJECT: GRB020331: Optical Observations of Afterglow Candidate
DATE:    02/04/08 17:15:16 GMT
FROM:    George Ricker at MIT  <grr@space.mit.edu>

GRB020331: Optical Observations of Afterglow Candidate

G. Monnelly, A. Dullighan, N. Butler, R. Vanderspek, G. Ricker (MIT)

write:

We observed the HETE error circle of GRB020331 (Ricker et al., GCN
#1315) with the Baade 6.5m telescope at Magellan on 2002 April 1.22 UT
using LDSS-2.  The observations took place 12.7 hours after the burst.
Seven 90s R-band exposures were used to mosaic the entire HETE error
circle. The limiting magnitude was R = 23.5, with 0.6" seeing.

We detect the afterglow candidate reported by Fox et. al. (GCN #1334)
at R = 21.05 +/- 0.11.  In comparison to their finding chart, the OT
is clearly separated in our image from the stellar object 3.9 arcsec
to the southeast, and we detect the reference star at R = 18.52 +/-
0.11.  Magnitudes are calibrated against star G020331 (R = 18.945)
from the photometry of Henden et. al. (GCN #1319).

Further, Fox et. al. (GCN #1334) report a weak detection of the
candidate on Mar 31.78, in observations having a limiting magnitude
of R ~ 19.5 mag.  If we take R = 19.5 as an upper limit on the magnitude
at this epoch, then our observations constrain the power law decay
index to be steeper than alpha = 0.8.

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