GCN Circular 1339
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. This message may be cited.