GCN Circular 3843
Subject
GRB 050820a: NIR Observations by WIRO
Event
Date
2005-08-21T05:51:50Z (20 years ago)
From
Daryl Macomb at Boise STate U <dmacomb@boisestate.edu>
Daryl Macomb, Jessica Elias (Boise State U.),
Jerry Bonnell, Alexander Kutyrev, Jay Norris (NASA/GSFC),
and Ron Canterna, Mike Pierce (U. Wyoming) report:
We observed the position reported by Fox and Cenko (GCN 3829)
of the afterglow for GRB 050820a (Swift trigger #151207, Page et al.,
GCN 3830) with the 2.3-meter WIRO telescope. Starting at 08:10 UT
(96 minutes after the GRB trigger) and continuing until 11:30 UT,
we detected the fading afterglow in the J band in each of 120 40-s
integrations. J magnitudes determined at the following times were
(relative to burst trigger):
Epoch T-Ttrig J mag
1 6240 s 16.0
2 9600 s 16.7
3 16020 s 16.9
Between epochs 1 and 2, the inferred average power-law decay index
is -1.5, steeper than the -0.9 index reported by Cenko and Fox
(GCN 3834) for the initial decay during the interval ~ 7 - 93 minutes
after the burst. Between epoches 2 and 3, the average decay index
flattens to -0.44, after which our observations ended due to twilight.
The times of the three reported epochs are arbitrary. Detailed
analysis to yield accurate break times and indices is in progress.