GCN Circular 21727
Klotz A., Turpin D., Atteia J.L. (CNRS-OMP-IRAP), Boer, M., Laugier, R. (CNRS-ARTEMIS), Gendre B. (UVI - Etelman Obs.) report: We imaged the field of GRB 170823A detected by SWIFT (trigger 769177) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France. The observations started 28s after the GRB trigger (18s after the notice). The elevation of the field decreased from 3 degrees above horizon and weather conditions were very good. The first image is trailed with a duration of 60.0s (see the description in Klotz et al., 2006, A&A 451, L39). We do not detect any OT with a limiting magnitude of: t0+28s to t0+88s : Rlim = 15.1 The second image is 30.0s exposure in tracking mode: t0+101s to t0+131s : Rlim = 15.1 We co-added a series of exposures: t0+101s to t0+395s : Rlim = 16.8 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction.