GCN Circular 30602
Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia and A. J. Castro-Tirado, M.D. Caballero-Garcia (IAA-CSIC), D. Hiriart and W. H. Lee (UNAM), C. J. Perez del Pulgar and I. Carrasco (UMA), I. H. Park (SKKU) on behalf of a larger collaboration, report: The 60cm BOOTES-5/JGT robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically responded in 16 min to the Swift trigger of GRB 210807A (Lien et al., GCNC 30600). The first image (1s exposure, clear-filter) was obtained at 10:20:19.5 UT. We detected the optical afterglow at the position reported by Swift /UVOT (Lien et al. GCNC 30600). In the co-added image (10 x 1s exposures) we measure 17.8+/- 0.2 mag. Further analysis is ongoing. The magnitude is calibrated against the USNO-B1 catalog and is not corrected for Galactic extinction in the direction towards the GRB. We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for its excellent support.