TITLE: GCN CIRCULAR NUMBER: 29993 SUBJECT: Fermi GRB 210510A: DDOTI Upper Limits on the Afterglow DATE: 21/05/11 19:55:18 GMT FROM: Emma Margarita Pereyra Talamantes at IA-UNAM Ensenada Margarita Pereyra (UNAM), Nat Butler (ASU), Alan M. Watson (UNAM), Eleonora Troja (GSFC/UMD), Simone Dichiara (GSFC/UMD), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Océlotl López, Diego Gonzalez (UNAM), Alexander Kutyrev (GSFC/UMD), and Srihari Ravi (ASU), report: We observed the field of the likely short Fermi GRB 210510A (trigger 642367205, GCN #29981, Fermi GBM Team) with the DDOTI/OAN wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir ( http://ddoti.astroscu.unam.mx) on 2021-05-11 from 03:24 to 10:45 UTC (8.1 to 15.4 hours after the event). We observed a region of 20.4 degrees in RA by 20.4 degrees in declination, with a 3 x 2 grid, centered on the Fermi GBM Final Position RA = 192.330, Dec = +44.860 (J2000 degrees). This region contains 6 instrumental fields or about 400 square degrees. We obtained 2280 to 2400 seconds of exposure per instrumental field in the w filter. We obtained AB photometry by calibration against the APASS catalog. We detect no likely candidate for the afterglow to our 10-sigma upper limits of w = 20.20 to 20.42 (interquartile range). We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.