TITLE:   GCN CIRCULAR
NUMBER:  30078
SUBJECT: Fermi GRB 210524B: DDOTI Upper Limits on the Afterglow
DATE:    21/05/25 16:25:45 GMT
FROM:    Emma Margarita Pereyra Talamantes at IA-UNAM Ensenada  <mpereyra@astro.unam.mx>

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

We observed the field of the likely long Fermi GRB 210524B  (trigger
643548039, GCN #30074, Fermi GBM Team) with the DDOTI/OAN wide-field imager
at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (
http://ddoti.astroscu.unam.mx) on 2021-05-25 from 03:32:24 to 04:48:24 UTC
(16.19 to 17.46 hours  after the event).

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: 148.460
DEC: 7.79 (J2000 degrees). This region contains 6 instrumental fields or
about 400 square degrees. We obtained 600 to 720 seconds of exposure per
instrumental field in the w filter. We obtained AB photometry by
calibration against the APASS catalog.

We detect no likely candidate for the afterglow to our 10-sigma upper
limits of w = 18.52 - 18.84 (inter-quartile).

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