GCN Circular 22846

Alan M. Watson (UNAM), Eleonora Troja (GSFC), 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), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz
(UCSC), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey
Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki
Toy (UMD) report:

We observed the field of GRB 180624A (Gibson et al., GCN Circ. 22832
Not found
 
 
)
with the Reionization and Transients Infrared Camera (RATIR;
www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio
Astron��mico Nacional on Sierra San Pedro M��rtir from 2018/06 25.26 to
2018/06 25.47 UTC (16.42 to 21.45 hours after the BAT trigger),
obtaining a total of 3.91 hours exposure in the r and i bands.

We detect a source in the enhanced Swift-XRT error circle (Goad et al.,
GCN Circ. 22835
Not found
 
 
) with the following magnitudes:

  r	= 21.03 +/- 0.02
  i	= 20.45 +/- 0.01

These magnitudes are calibrated against the SDSS DR9 catalog, are in the
AB system, and are not corrected for Galactic extinction in the
direction of the GRB.

We note that the source has faded significantly from the earlier
observations of Guidorzi et al. (GCN Circ. 22839
Not found
 
 
) of r = 19.9 +/- 0.1 at
0.54 hours and Schady (GCN Circ. 22840
Not found
 
 
) of r = 20.2 +/- 0.1 at 15.07
hours. We also see the source fade by about 0.5 mag in each our bands
during the course of our observations.

We confirm the observation of Rossi et al. (GCN Circ. 22845
Not found
 
 
) that the
source is a couple of arcsec to the SE of the SDSS galaxy
J211223.25-022015.9.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.