TITLE: GCN CIRCULAR NUMBER: 8764 SUBJECT: GRB 090102: TAROT Calern observatory optical light curve DATE: 09/01/02 05:14:46 GMT FROM: Alain Klotz at CESR-CNRS Klotz, A. (CESR-OMP), Gendre, B. (OAMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report: We analyzed images of GRB 090102 detected by SWIFT (trigger 338895) with the TAROT at the Calern observatory, France. In our previous GCN Circ. (9761) we made a mistake in the celestial coordinates of the optical afterglow. TAROT position is compatible with UVOT (Mangano et al. GCNC 8762). The first image is trailed with a duration of 60.0s (see the description in Klotz et al., 2006, A&A 451, L39) and we detect the growth of the optical light curve that culminates at t0+60s (+/- 3s) with a brightness R=13.4 (i.e. ~40s after the end of the gamma activity). We calibrated magnitudes in R band using NOMAD1 1231-0209716 (R=13.31). After t0+60s, the decay of the afteglow is classic with a decay of alpha=1.6 +/- 0.2. Hereafter, TAROT Calern data (tstart and tend are expressed in seconds after the BAT trigger t0): tstart tend R dR 40.8 46.8 14.3 0.2 46.8 52.8 13.6 0.1 52.8 58.8 13.4 0.1 58.8 64.8 13.4 0.1 64.8 70.8 13.5 0.1 70.8 76.8 13.7 0.1 76.8 82.8 13.7 0.1 82.8 88.8 14.0 0.1 88.8 94.8 14.1 0.1 94.8 100.8 14.3 0.1 107.6 137.6 14.4 0.2 144.6 174.6 14.9 0.2 181.6 211.6 15.5 0.3 Further observations are in progress