TITLE:   GCN CIRCULAR
NUMBER:  30698
SUBJECT: GRB 210822B: DDOTI Upper Limits on the Afterglow
DATE:    21/08/23 21:39:19 GMT
FROM:    Kin O. C. L. Mendoza at Instituto de Astronoma, UNAM  <koclopez@astro.unam.mx>

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

We observed the field of the Fermi - GBM event GRB 210822B (Fermi
Collaboration, GCN Circ. 30683) with the DDOTI wide-field imager at the
Observatorio Astronómico Nacional on Sierra San Pedro Martir (
http://ddoti.astroscu.unam.mx) from 2021-08-23 05:28:21 to 06:11:11 UTC
(12.85to 13.73 hours after the trigger).

We observed a region of 20.4 degrees in RA by 20.4 degrees in declination,
with a 3 x 2 grid, centered on the Fermi GBM Final Position RA:  238.17,
DEC: +18.02 (J2000 degrees). This region contains 6 instrumental fields or
about 400 square degrees. We obtained 7.77 minutes of exposure per
instrumental field in the w filter. We obtained AB photometry by
calibration against the APASS catalog.


Comparing to the Pan-STARRS DR1 catalog, we detect no uncatalogued point
sources to a 10-sigma limiting magnitude of w = 18.07 - 18.65

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