GCN Circular 18956

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
(GSFC/STScI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jos�� A. de Diego (UNAM), Leonid Georgiev (UNAM),
Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Neil Gehrels (GSFC),
Harvey Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and
Vicki Toy (UMD) report:

We observed the field of GRB 160131A (Page et al., GCN Circular 18951
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 2016/01 31.35 to
2016/01 31.37 UTC (0.07 to 0.50 hours after the BAT trigger), obtaining
a total of 0.18 hours exposure in the r, i, and z bands.

We detect a bright uncatalogued source at 05:12:40.33 -07:03:00 (J2000,
��0.5 arcsec). In comparison with the USNO-B1 catalog, we obtain the
following mean magnitudes:

 r	= 13.35 �� 0.04
 i	= 13.01 �� 0.02
 z	= 12.67 �� 0.04

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

The source fades roughly as t^-0.87 during our observations. This source
is presumably the optical counterpart reported by Page et al. (GCN
Circular 18951
Not found
 
 
), Yurkov et al. (GCN Circular 18952
Not found
 
 
), Guidorzi et al.
(GCN Circular 18953
Not found
 
 
), and Xin et al. (GCN Circular 18954
Not found
 
 
).

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