TITLE: GCN CIRCULAR NUMBER: 29998 SUBJECT: GRB 210511B: DDOTI Upper Limits on the Afterglow DATE: 21/05/12 00:14:52 GMT FROM: Kin O. C. L. Mendoza at Instituto de Astronoma, UNAM Océlotl Lopez (UNAM), Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Simone Dichiara (GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM), Srihari Ravi (ASU), and Eleonora Troja (GSFC/UMD) report: We observed the field of the Fermi - GBM event GRB 210511B (Fermi Collaboration, GCN Circ. 29988) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Martir ( http://ddoti.astroscu.unam.mx) from 2021-05-11 11:49:26 to 12:01:38 UTC (0.38 to 0.58 hours after the trigger) and obtained 6 minutes of exposure in the w filter. The images were obtained after the astronomical twilight. We observed a region covering approximately 14 degrees in RA and 10 degrees in declination, with a 2 x 1 grid, including the entire initial uncertainty region distributed in the GCN Notice (Fermi Collaboration, GCN Circ. 29988) Comparing to the Pan-STARRS DR1 catalog, we detect no uncatalogued point sources to a 10-sigma limiting magnitude of w = 18.39. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Martir.