TITLE:   GCN CIRCULAR
NUMBER:  17096
SUBJECT: GRB 141121A: RATIR Optical Observations - Fading Again
DATE:    14/11/24 18:04:30 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>

Nat Butler (ASU), Alan M. Watson (UNAM), 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 24.27 to 2014/11 24.53 UTC (74.70
to 80.86 hours after the BAT trigger), obtaining a total of 4.93 hours
exposure in the r, i, and z band.

For a source within the Swift-XRT error circle, in comparison with the
SDSS DR9, we obtain the following detections and upper limits
(3-sigma):

r = 20.68 +/- 0.03
i = 20.51 +/- 0.04
z > 20.48

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

The afterglow has faded by about 0.08 magnitudes in r and i compared
to our observations at 54 hours (Watson et al., GCN 17090). This
corresponds to a shallow decay close to t^-0.2. Thus, the
rebrightening reported by Watson et al. (GCN 17090) and confirmed by
Dichiara et al. (GCN 17092) appears to have ended.

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