TITLE: GCN GRB OBSERVATION REPORT NUMBER: 796 SUBJECT: GRB000911: Optical Transient DATE: 00/09/19 23:51:27 GMT FROM: Paul Price at RSAA, ANU at CIT P.A. Price (RSAA,ANU/Caltech), T.J. Galama (Caltech), R.W. Goodrich (W.M. Keck Observatory) and A. Diercks (Caltech) report on behalf of a larger collaboration: "We have observed the optical transient candidate of GRB000911 (Berger et. al., GCN #795) with the Keck II telescope + ESI, starting at Sep 15.59 UT. We took 5 x 120 second images in 0.6 arcsec seeing. We have compared the combined image with the R_MACHO (~ Cousins R) image from the MSO 50-inch telescope (Price et. al., GCN #793), using the USNO-A2.0 star U0975_00513791 (RA2000, Dec2000 = 02:18:33.18, +07:45:47.6) with assumed R = 18.6. Results are: Telescope Epoch Magnitude MSO50+MACHO Sep 12.73 20.257 +/- 0.167 Keck+ESI Sep 15.59 21.911 +/- 0.053 (Errors are purely statistical.) In the Keck+ESI image, the candidate is located at (RA2000, Dec2000) = (02:18:33.21, +07:45:47.86) +/- (0.34", 0.31") and has a PSF consistent with a point source. From these figures, we calculate a decay constant of alpha = 1.4. In the light of the fading nature of the candidate, it is likely the optical transient associated with GRB000911." This message may be cited.