TITLE: GCN CIRCULAR NUMBER: 29760 SUBJECT: GRB 210404.141: DDOTI Upper Limits DATE: 21/04/04 17:59:16 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 Fermi/GBM GRB 210404.141 (trigger 639199407) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-04 04:37 UTC to 2021-04-04 12:14 UTC (from 1.2 to 8.9 hours after the trigger). We observed a region covering aproximately 21 degrees in RA and 20 degrees in declination (about 420 square degrees) centered on the Fermi GBM ground position of 12:26:43 -01:18:00 (J2000). We obtained between 2600 and 3400 seconds of exposure per pointing in the w filter. We calibrated our images against the APASS catalog. We do not detect any fading sources to our 10-sigma limit, which varies over the field between 20.31 and 20.71. We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.