GCN Circular 4972
Subject
GRB 060418, SMARTS continuing afterglow observations
Date
2006-04-18T07:22:10Z (18 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
B. E. Cobb (Yale), part of the larger SMARTS consortium, reports:
Continuing ANDICAM observations (see GCN 4970 for observing details) of
the afterglow of GRB 060418 (Falcone et al. GCN 4966) record the steady
fading behavior of the afterglow between all 45-second individual I-band
exposures, as shown below. These preliminary magnitudes were
calibrated using several USNO-B1.0 stars and the error in the photometric
calibration is ~0.2 mag. The relative error is ~0.05 magnitudes.
time
post-burst I-magnitude
1.09 16.50
1.17 16.66
1.41 16.79
1.48 16.85
2.25 17.44
2.32 17.49
2.57 17.61
2.64 17.71
3.17 17.79 (225-second exposure)
3.34 17.99 (225-second exposure)
The decay rate is, therefore, approximately alpha = -1.2 between about 1
and 3 hours post-burst. This is similar to the power law index
calculated by Nysewander et al. (GCN 4971) during the first hour
post-burst and suggests that no jet break has yet been observed.