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GCN Circular 1303

Subject
GRB011211 revised BVRI field photometry
Date
2002-03-23T18:57:09Z (22 years ago)
From
Arne A. Henden at USNO/USRA <aah@nofs.navy.mil>
A. Henden (USRA/USNO) reports on behalf of the USNO GRB team:

We have acquired additional BVRcIc all-sky photometry for
an 11x11 arcmin field that is approximately centered on
the position of the optical transient for GRB011211 reported
by Grav et al. (GCN 1191) with the USNOFS 1.0-m telescope.
The field was observed on two more nights,
with the new dataset posted at:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb011211.dat
Stars brighter than V=13.5 are saturated and should be used with care.
The current photometry has a potential external zero-point
error of about one percent.  The astrometry in this file
is based on linear plate solutions with respect to USNO-A2.0.
The internal errors are less than 100mas.

The two new nights have shown that the photometry
reported in GCN 1197 has larger error than originally estimated,
most likely caused by a combination of the very poor seeing,
high airmass and approaching dawn.  For example, the
comparison star U0675_11427359 that was used by Grav et al.and
Jensen et al. (GCN 1195) to calibrate their field can be found
in the new .dat file with the following magnitudes:

GCN 1195 (Jensen)   B = 18.65  V = 18.18  R = 17.90  I = 17.07
GCN 1197 (Henden)   B = 18.65  V = 18.11  R = 17.76  I = 17.42
new result          B = 18.48  V = 18.00  R = 17.70  I = 17.37

We apologize for the lateness of this correction, but this
winter has had unusually few photometric nights.  This is
the first case in several dozen calibrations that we have
performed for the GRB community in which the final dataset
differed from the initial dataset by more than a couple of percent.
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