TITLE: GCN CIRCULAR NUMBER: 30844 SUBJECT: GRB 210912A: BOOTES-5/JGT optical afterglow candidate (Correction to GCNC 30823) DATE: 21/09/17 11:55:37 GMT FROM: Youdong HU at IAA-CSIC <huyoudong072@hotmail.com> Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado, R. Sanchez-Ramirez 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: The 60cm BOOTES-5/JGT robotic telescope at Observatorio Astronomico Nacional in San Pedro Martir (Mexico) automatically responded in 13 s to the Swift trigger for GRB 210912A (Troja et al., GCNC 30820). In the co-added clear image (30 x 1 s), we find an uncataloged optical source at (J2000) coordinates RA: 8:39:34.30, DEC:+79:13:17.5, which is located at the edge of the XRT error box (Troja et al., GCNC 30820) and for which we measure R = 18.5 mag. We propose this source to be the GRB 210912A optical afterglow, pending confirmation of its variability. Further observations are ongoing. We thank the staff at San Pedro Martir for their support. In the GCNC 30823, we have a typo of the GRB name in the text and it was corrected now. We apologize for the possible confusion and inconvenience.