TITLE:   GCN CIRCULAR
NUMBER:  29680
SUBJECT: GRB 210321A: DDOTI Afterglow Confirmation
DATE:    21/03/21 14:54:00 GMT
FROM:    Nat Butler at Az State U  <natbutler@asu.edu>

Nat Butler (ASU), Alan M. Watson (UNAM), 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 210321A (Dichiara et al., GCN
Circ.  29677) with the DDOTI wide-field imager at the Observatorio
Astronómico Nacional on Sierra San Pedro Martir (
http://ddoti.astroscu.unam.mx) starting at 2021-03-21 08:56 UTC (from 1.7
hours after the trigger).

We observed a region covering approximately 7 degrees in RA and 10 degrees
in declination (about 70 square degrees) centered on the XRT position
(Perri et al., GCN 29678) in the w filter.

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 =
18. This confirms the afterglow reported in UVOT observations by Siegel et
al. (GCN Circ.  29679).

We thank the staff of the Observatorio Astronomico Nacional in San Pedro
Martir.