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GCN Circular 1346

GRB020331: Confirmation of Afterglow Candidate with Magellan
2002-04-09T15:28:42Z (22 years ago)
George Ricker at MIT <>
GRB020331: Confirmation of Afterglow Candidate with Magellan

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


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 

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.

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