TITLE:   GCN CIRCULAR
NUMBER:  22446
SUBJECT: GRB 180224A: RATIR Optical Observations 
DATE:    18/02/25 17:01:05 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>

Alan M. Watson (UNAM), Nat Butler (ASU), 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 180224A (Lien et al., GCN 22442) 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 2018/02 25.23 to 2018/02 25.53
UTC (7.24 to 14.42 hours after the BAT trigger), obtaining a total of
3.91 hours exposure in the r and i bands.

We detect a source at 13:30:44.11 38:04:44.2 (J2000, ± 0.5 arcsec),
within the Swift-XRT error circle, in comparison with the SDSS DR9, with
the following magnitudes:

  r	= 22.94 +/- 0.13
  i	= 22.08 +/- 0.06

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

The position and magnitudes of this source are consistent with the SDSS
DR9 galaxy SDSS J133044.06+380443.0, which has r = 22.56 +/- 0.18 and i
= 21.83 +/- 0.14. We suggest that this might be the host galaxy of the
GRB.

Vladimirov et al. (GCN 22444) report a early 16.1 mag transient in the
Swift XRT error circle. Our non-detection 7 hours later suggests that
the afterglow faded extremely quickly.

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