Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC),
William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (UCB), 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 160121A (Hagen et al., GCN Circular 18912)
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 22.13 to
2016/01 22.29 UTC (13.28 to 17.14 hours after the BAT trigger),
obtaining a total of 2.92 hours exposure in the r, i, and z bands.
We detect a source at 07:16:21.16 -23:35:31.5 J2000 (�0.5 arcsec),
consistent with the enhanced Swift-XRT position (Osborne et al., GCN
Circular 18918). In comparison with the USNO-B1 and 2MASS catalogs, we
obtain the following magnitudes and 3-sigma upper limits:
r = 21.73 � 0.13
i = 21.10 � 0.08
z > 19.80
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
Our observations have almost the same midpoint as the GROND observations
reported by Delvaux et al. (GCN Circular 18921). The i band observations
are consistent, but our r band measurement is surprisingly 0.6 mag
fainter than theirs.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro