TITLE: GCN CIRCULAR NUMBER: 23018 SUBJECT: GRB 180721A: BOOTES-5/JGT optical observations DATE: 18/07/22 20:55:42 GMT FROM: Irene Carrasco at Inst.De Astrofisica de Andalucia I. Carrasco (Univ. de Malaga), Y. Hu, E. Fernandez-Garcia, J. C. Tello and A. J. Castro-Tirado (IAA-CSIC), D. Hiriart and W. H. Lee (UNAM), S. Jeong and I. H. Park (SKKU), M. D. Caballero-Garcia (ASU-CAS, CZ) and R. Cunniffe (Inst. of Physics, CZ) 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 21s (and 53s after the GRB onset) to the Swift trigger of GRB 180721A (Sbarufatti et al., GCNC 22994). The first image (10s exposure, r-band) was obtained at 11:07:10 UT. At the position of the Swift X-ray afterglow (Goad et al. GCNC 22997), no optical afterglow is detected down 18.1 mag. Furthermore, on the co-add of the images obtained until 11:33:52 UT no afterglow is detected down to 21 mag, consistent with the limit reported by Guidorzi et al. (GCNC 22995). We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for its excellent support.