TITLE:   GCN CIRCULAR
NUMBER:  17128
SUBJECT: GRB 141121A: Continued RATIR Optical Observations
DATE:    14/12/01 16:07:08 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), Chris Klein (UCB), Ori Fox (UCB), J.
Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), José
A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos
Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report:

We observed the field of GRB 141121A (Lien et al., GCN 17075) 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 2014/12 1.30 to 2014/12 1.54 UTC (243.35 to 249.19 hours after
the BAT trigger), obtaining a total of 4.56 hours exposure in the r, i, and z
bands.

For a source within the Swift-XRT error circle, in comparison with the SDSS, we
obtain the following detections and upper limits (3-sigma):

r = 22.38 +/- 0.16
i = 22.21 +/- 0.16
z > 20.41

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

Compared to our observations on previous nights (Watson et al., GCN 17116;
Butler et al., GCN 17119), the fading appears to be slowing and is now behaving
as t^-0.5. This may be evidence for an underlying host galaxy more closely
coincident with the GRB than the candidate reported by Watson et al. (GCN
17105).

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