[vsnet-grb-info 20701] GRB 180620A: RATIR Optical Afterglow Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22799
SUBJECT: GRB 180620A: RATIR Optical Afterglow Detection
DATE:    18/06/20 09:16:28 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), Michael G. Richer (UNAM), Ori Fox (STScI),
J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara
(UVI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM),
Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and
Vicki Toy (UMD) report:

We observed the field of GRB 180620A (Evans, et al., GCN 22798) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2018/06 20.36 to 2018/06 20.38 UTC (0.03
to 0.47 hours after the BAT trigger), obtaining a total of 0.36 hours
exposure in the r and i bands.

For a source within the Swift-XRT error circle, in comparison with the
USNO-B1 and 2MASS catalogs, we
obtain the following detections:

  r	= 18.01 +/- 0.01
  i	= 17.71 +/- 0.01

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  We observe the rise and
initial decline of the afterglow.

We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.  Further observations are planned.