TITLE: GCN CIRCULAR NUMBER: 30742 SUBJECT: GRB 210827A: BOOTES-5/JGT optical upper limit DATE: 21/08/29 16:06:32 GMT FROM: Youdong HU at IAA-CSIC <huyoudong072@hotmail.com> Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado and 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: We triggered the 60cm BOOTES-5/JGT robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) for the Fermi trigger of GRB 210827A (Fermi GBM team, GCNC 30724) in order to monitor the Swift/BAT-GUANO error region (DeLaunay et al. GCNC 30732) on 28 Aug 05:25 UT (~ 0.81 day after trigger). In the co-added clear image (8 x 60 s), no optical afterglow is detected within the BAT error region or at the source 3 position later reported by the Swift-XRT (Evans et al., GCNC 30733; Gropp et al., GCNC 30734) down to 19.7 mag. This non-detection is consistent with the report by MASTER-Net (Lipunov et al., GCNC 30736). We thank the staff at Observatorio Astronomico Nacional in San Pedro Martir for its excellent support.