TITLE:   GCN CIRCULAR
NUMBER:  29752
SUBJECT: GRB 210402A: DDOTI Upper Limits
DATE:    21/04/03 15:04:05 GMT
FROM:    Alan M Watson at UNAM  <alan@astro.unam.mx>

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 210402A (Page et al., GCN Circ.
29743) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional
on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) from 2021-04-03 02:52
UTC to 2021-04-03 12:18 UTC (from 4.8 to 14.2 hours after the trigger).

We observed a region covering aproximately 7 degrees in RA and 10 degrees in
declination (about 70 square degrees), including the XRT position in the w
filter, and obtained 23ks of exposure. We calibrated our images against the
APASS catalog.

Compared to the USNO-B1, Pan-STARRS DR1, and APASS DR10 catalogs, we do not
detect a source at the X-ray position to a 3-sigma limiting magnitude of w =
23.2.

Our non-detection is consistent with the non-detections reported by Zhu et al.
(GCN Circ. 29745) and Leonini et al. (GCN Circ. 29747).

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