TITLE: GCN CIRCULAR NUMBER: 30135 SUBJECT: Fermi GRB 210606A: DDOTI Upper Limits on the Afterglow DATE: 21/06/06 19:29:35 GMT FROM: Emma Margarita Pereyra Talamantes at IA-UNAM Ensenada Margarita Pereyra (UNAM), Alan M. Watson (UNAM), Nat Butler (ASU), Camila Angulo, Simone Dichiara (GSFC/UMD), Rosa L. Becerra (UNAM), William H. Lee (UNAM), Océlotl López, Eleonora Troja (GSFC/UMD), Diego Gonzalez (UNAM), Alexander Kutyrev (GSFC/UMD), and Srihari Ravi (ASU), report: We observed the field of the likely Long Fermi GRB 210606A (trigger 644644567, GCN #30131, 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 2021/06/06 from 04:12:31.000 to 06:46:24.000 UTC (0.27 to 2.83 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: 177.630000, DEC: -0.470000 (J2000 degrees). This region contains 6 instrumental fields or about 400 square degrees. We obtained 1075 to 1200 seconds of exposure per instrumental field in the w filter. We obtained AB photometry by calibration against the APASS catalog. We detect no likely candidates for the afterglow to our 10-sigma upper limits of w = 19.64 to 19.93 (inter-quartile). We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir.