[vsnet-grb-info 28280] GRB 210704A: DDOTI upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30383
SUBJECT: GRB 210704A: DDOTI upper limit
DATE:    21/07/05 18:47:55 GMT
FROM:    Simone Dichiara at UMCP/NASA/GSFC  <dichiara at umd.edu>

Simone Dichiara (GSFC/UMD), Eleonora Troja (GSFC/UMD), Nat Butler (ASU),
Alan M. Watson  (UNAM), Rosa L. Becerra (UNAM),  Alexander Kutyrev
(GSFC/UMD), William H. Lee (UNAM),
Océlotl Lopez (UNAM), Diego Gonzalez (UNAM), Margarita Pereyra (UNAM) and
Srihari Ravi (ASU) report:

We observed the field of the Fermi/LAT GRB 210704A (Berretta et al. GCN
Circ. 30375, Ursi et al. GCN Circ. 30372, Malacaria et al. GCN Circ. 30380)
with the DDOTI wide-field imager at the Observatorio Astronómico Nacional
on Sierra San Pedro Martir (http://ddoti.astroscu.unam.mx) starting from
2021-07-05 04:51 to 05:01 UTC (from 9 hours after the trigger). We obtained
a 360 seconds of total exposure in the w filter.

We find no new sources within the XRT error region reported by D'Ai et al.
(GCN Circ. 30379) . Calibrating our images against the APASS catalog we
obtained a 5-sigma limiting magnitude of w = 19.7.
Compared to the USNO-B1, Pan-STARRS DR1, and APASS DR10 catalogs, we detect
no uncataloged sources to our limit.

We also noticed the presence of a galaxy cluster at z~0.2 coincident with
the afterglow localization region and the presence of a bright galaxy about
30" north from the X-ray transient.

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