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GCN Circular 3727

Subject
GRB 050730, corrected photometry and break?
Date
2005-08-01T20:39:19Z (19 years ago)
From
Peter Garnavich at U of Notre Dame <pgarnavi@nd.edu>
M. Holman (CfA), P. Garnavich (Notre Dame), K.Z. Stanek (Ohio State)

The photometry of the GRB 050730 afterglow and comparison
star reported on GCN 3716 requires correction. The CCD gain
between the standard star and GRB observations differed by 20%.
The IMACS photometry of the afterglow taken on July 30 23:57 (UT)
should be R=17.73 +/-0.05 mag and the comparison star at
14:08:14.62 -03:46:29 (2000) has R=17.41 +/-0.05 mag.

The photometry of Burenin et al. (GCN 3718) based on our old
calibration should be made 0.23 mag fainter. Even
without these corrections, the R-band observations
imply a power-law decay index of -1.7 between 4 hours and
23 hours after the burst. This is much steeper than the V-band
index suggested by Swift UVOT photometry (Blustin et al. GCN 3717).
The Swift V-band data between 12 minutes and 6.5 hours after
the burst is consistent with a power-law decay index of -0.9.
If the spectral index has not changed significantly,
then the combined Swift and ground data suggests a steepening
in the power-law decay occurred between 6 hours and 23 hours
post-burst.
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