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GCN Circular 4972

GRB 060418, SMARTS continuing afterglow observations
2006-04-18T07:22:10Z (18 years ago)
Bethany Cobb at Yale U <>
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.

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.
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