[vsnet-grb-info 28569] GRB 210820A: RATIR Optical Detections

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30672
SUBJECT: GRB 210820A: RATIR Optical Detections
DATE:    21/08/21 15:52:28 GMT
FROM:    Nat Butler at Az State U  <natbutler at asu.edu>

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H.
Lee (UNAM), Eleonora Troja (GSFC), Michael G. Richer (UNAM), Ori Fox
(STScI),
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Enrico Ramirez-Ruiz (UCSC),
Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC),
Rosa
L. Becerra (UNAM), Simone Dichiara (UMD), and Océlotl López (UNAM) report:

We observed the field of GRB 210820A (Beardmore, et al., GCN 30664) with
the
Reionization and Transients Infrared Camera (RATIR) on the 1.5m Harold
Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San
Pedro Mártir from 2021/08 21.27 to 2021/08 21.50 UTC (12.47 to 17.96
hours after the BAT trigger), obtaining a total of 3.70 hours exposure
in the r and i bands.

We detect one source within the Swift-XRT error circle (Beardmore, et al.,
GCN 30667).  In comparison with the SDSS DR9 and 2MASS catalogs, we obtain:

  r = 22.84 +/- 0.22
  i = 22.66 +/- 0.18

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

The source is located at RA, Dec = 1:22:33.47, +4:36:28.1 (J2000, +/-0.5").
This is 0.2 arcsec away from the UVOT OT (GCN 30664).

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