TITLE: GCN CIRCULAR NUMBER: 29598 SUBJECT: GRB 210306A: DDOTI Afterglow Confirmation DATE: 21/03/06 04:28:38 GMT FROM: Alan M Watson at UNAM Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Simone Dichiara (GSFC/UMD), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl Lopez (UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM), Srihari Ravi (ASU), and Eleonora Troja (GSFC/UMD) report: We observed the field of the Swift/BAT GRB 210306A (D'Elia et al., GCN Circ. 29597) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) starting at 2021-03-06 04:07 UTC (from 14 minutes after the trigger). We observed a region covering aproximately 7 degrees in RA and 10 degrees in declination (about 70 square degrees) centered on the XRT position in the w filter. We calibrated our images against the APASS catalog. Compared to the USNO-B1, Pan-STARRS DR1, and APASS DR10 catalogs, we detect a bright source at 08:39:50.04 +60:12:18.9 (J2000) fading from about w = 17. This confirms the afterglow reported in UVOT observations by D'Elia et al. (GCN Circ. 29597) We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.