TITLE: GCN CIRCULAR NUMBER: 11382 SUBJECT: GRB 101024A: Zadko observatory - Gingin. Optical observations refined analysis DATE: 10/10/26 08:46:02 GMT FROM: Myrtille LAAS-BOUREZ at U.Western Australia GRB 101024A: Zadko observatory - Gingin. Optical observations refined analysis ------------------------------------------------------------------------------- M. Laas-Bourez (UWA/ICRAR), A. Klotz (CESR-UPS-CNRS), D. Coward (UWA), D. Blair (UWA), M. Boer (OHP-CNRS), P. Thierry (CESR-UPS-CNRS) report: We analyzed carefully early images of GRB101024A taken with the Zadko telescope, Gingin, Australia (see Laas-Bourez et al. 2010 GCNC 11380). Images are unfiltered. Magnitudes are converted into R band using the star NOMAD1 0127-0023961 R=13.61 supposing (V-R)=0.6 for the optical counterpart of the GRB. Magnitudes are not corrected for galactic dust extinction. ------------------------------- start end Rmag (s) (s) ------------------------------- 215 222 16.55 +/-0.15 222 245 16.72 +/-0.15 259 289 16.86 +/-0.12 305 335 17.06 +/-0.12 349 379 17.24 +/-0.12 394 424 17.23 +/-0.12 ------------------------------- Considering a law decay in flux proportional to t^-alpha, there is a consistent decrease with alpha ~ 1.1 between 215 and ~ 360 seconds. After 360 seconds, a plateau seems to be reached lasting at least 60 seconds. Compared to the UVOT data taken in the same range of time (De Pasquale et al. 2010 GCNC 11375) the optical afterglow is very red, consistent with a redshift z>2. This message may be cited.