TITLE:   GCN CIRCULAR
NUMBER:  1125
SUBJECT: GRB010921, optical observations
DATE:    01/11/01 18:06:54 GMT
FROM:    Don Lamb at U.Chicago  <lamb@oddjob.uchicago.edu>

D. Q. Lamb, B. C. Lee, D. L. Tucker, D. E. Vanden Berk, P. Newman,
J. Krzesinski and A. N. Kleinman, on behalf of the SDSS GRB team,
report:

We observed the HETE error box for GRB 010921 (GCN 1096) using the SDSS
0.5-m "Photometic Telescope" at APO under partly cloudy conditions on
2001 September 22 beginning at UT 02:36 and on 2001 September 23
beginning at UT 05:23.  Images of the entire improved HETE error box
(GCN 1097) were acquired in the SDSS u, g , r, i, and z filters on both
nights.

The optical transient (OT) reported by Price et al. (GCN 1107; see also
GCN 1108 and GCN 1113) was r'=19.6 +/-0.3 on September 22 and
significantly fainter on September 23 (we place an upper limit on r' of
roughly 20.0).  The OT is marginally visible (at perhaps the 1 to 2
sigma level) in g and i on September 22 and in g and r on September 23.
We place upper limits on u, g, i, and z of roughly 20.5, 18.5, 17.5,
and 15.0 on September 22, with the completeness limit of the i and z
filters heavily degraded by clouds, and 19.5, 20.0, 18.5, and 18.5 on
September 23, again impacted by clouds.  These upper limits are
consistent with a ~ nu^{-2.3} spectrum over u, g, r, i, and z (GCN
1107).  Images can be found at http://sdss.fnal.gov:8000/grb/.

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