GCN Circular 21903
Klotz A., Atteia J.L. (CNRS-OMP-IRAP), Boer, M., Laugier, R. (CNRS-ARTEMIS), Gendre B. (UVI - Etelman Obs.) report: We imaged the field of GRB 170921A detected by SWIFT (trigger 773509) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France. The observations started 3.86h after the GRB trigger. The elevation of the field increased from 12 degrees above horizon and weather conditions were good. We co-added a series of exposures. No OT is detected with a limiting magnitude of: t0+3.86h to t0+4.23h : Rlim = 19.5 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction.