TITLE: GCN CIRCULAR NUMBER: 13215 SUBJECT: GRB 120403B: TAROT La Silla observatory optical observations DATE: 12/04/04 16:39:02 GMT FROM: Alain Klotz at CESR-CNRS Klotz A. (IRAP-CNRS-OMP), Gendre B. (ASDC/INAF-OAR), Boer M. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report: We imaged the field of GRB 120403B detected by SWIFT (trigger 519256) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 2.8h after the GRB trigger (the burst occured during the afternoon). The elevation of the field was 29 degrees above horizon and weather conditions were good. We co-added a series of exposures. No optical counterpart was found. The limiting magnitude of the image is R=19.5 but the burst occured close to a R=17.2 star. So we prefer to publish a conservative value of 18.2 as the upper limit of the afterglow: start stop 2.95h 4.82h R > 18.2 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction. This message may be cited.