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GCN Circular 4972

Subject

GRB 060418, SMARTS continuing afterglow observations

Event

GRB 060418

Date

2006-04-18T07:22:10Z (19 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 4970Loading...
 
  for observing details) of 
the afterglow of GRB 060418 (Falcone et al. GCN 4966Loading...
 
 ) 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 4971Loading...
 
 ) during the first hour 
post-burst and suggests that no jet break has yet been observed.