TITLE:   GCN CIRCULAR
NUMBER:  17084
SUBJECT: GRB 141121A: RATIR Optical Observations
DATE:    14/11/21 17:02:31 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 2014/11 21.33 to 2014/11 21.53 UTC (4.00 to 8.84 hours after
the BAT trigger), obtaining a total of 3.78 hours exposure in the r, i and z
bands.

For a source within the Swift-XRT error circle, in comparison with the SDSS DR9,
we obtain the following detections:


r	19.62 +/- 0.02
i	19.45 +/- 0.02
z	19.76 +/- 0.12

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

Over the course of our observations, the flux in r and i fades slightly as
t^-0.15, with t measured from the time of the BAT trigger. Our measurements in z
are noisier, but consistent with this shallow decay.

We confirm this as the afterglow reported by Tanga et al. (GCN 17078) and
Dichiara et al. (GCN 17082), for which Perley et al. (GCN 17081) report a
spectroscopic redshift of 1.47.

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

The RATIR team congratulates the Swift team on 10 years of operation.