TITLE: GCN CIRCULAR NUMBER: 1125 SUBJECT: GRB010921, optical observations DATE: 01/11/01 18:06:54 GMT FROM: Don Lamb at U.Chicago 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/. This message is quotable.