GCN Circular 1346
GRB020331: Confirmation of Afterglow Candidate with Magellan A. Dullighan, G. Monnelly, N. Butler, R. Vanderspek, G. Ricker (MIT) write: We obtained second epoch observations of the HETE error circle of GRB020331 (Ricker et al., GCN #1315) with the Baade 6.5m telescope at Magellan on 2002 April 9.06 UT using LDSS-2. The observations took place 8.37 days after the burst, and 7.84 days after our first epoch observations (Monnelly et al., GCN #1339). Two 200s R-band exposures were used to image a 7.5 arcmin diameter region centered on the coordinates of the afterglow candidate first reported by Fox et. al. (GCN #1334). In our second epoch observations, we detect the afterglow candidate at R = 22.9 +/- 0.14. In comparison to our first epoch measurement, with exactly the same instrument configuration, the afterglow candidate has declined by 1.8 +/- 0.2 magnitudes in R. As in our first epoch observations, magnitudes are calibrated against star G020331 (R = 18.945) from the photometry of Henden et. al. (GCN #1319). Combining our first and second epoch observations, the power law decay index of the afterglow candidate is well-determined as alpha = 0.62 +/- 0.1. We conclude that the Fox et al candidate is indeed the optical afterglow of GRB020331. This message may be cited.