TITLE:   GCN CIRCULAR
NUMBER:  29935
SUBJECT: Fermi GRB 210503A: DDOTI Upper Limits on the Afterglow
DATE:    21/05/04 22:48:23 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 210503A (trigger
641763254, GCN #29927, 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 2021-05-04 from 07:02 to 11:38 UTC (11.5
to   16 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 328.93d
+66.03d (J2000). This region contains 6 instrumental fields or about 400
square degrees. We obtained 1560 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 = 19.32 to 19.93 (interquartile range).

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

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