[vsnet-grb-info 27657] GRB 210404.141: DDOTI Upper Limits

[GCN Circulars]

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 at astro.unam.mx>

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.