TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  987
SUBJECT: GRB010222, field photometry
DATE:    01/02/25 00:44:50 GMT
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 preliminary UBVRcIc all-sky photometry for
the field of GRB010222 with the USNOFS 1.0-m telescope on one
photometric night with poor seeing.  This 11x11arcmin field includes
the proposed counterpart and extends to approximately V=20.
All stars brighter than V=14 are saturated and should be used
with care.  We have placed the photometric data on our
anonymous ftp site:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb010222.dat
The current photometry has a potential external zero-point
error of about two percent that needs to be added in
quadrature to the Poisson errors given in the datafile and
also below.  The astrometry in this file is based on linear
plate solutions with respect to USNO-A2.0. The internal errors
are less than 100mas.

In particular, the values for the two comparison stars noted
in the literature are:

      ID           U       B       V       Rc      Ic
Henden A GCN967  13.311  14.318  14.570  14.688  14.829
                  0.002   0.002   0.002   0.002   0.004

Stanek A GCN970  18.680  18.349  17.613  17.175  16.761
                  0.045   0.014   0.010   0.015   0.017

Note that Henden star A has nearly identical R-magnitude to
the value listed in USNO-A2.0, whereas observations made with
respect to Stanek star A will have to be adjusted fainter.

At least two additional nights of photometry will be added to the data
file when weather conditions permit.