TITLE:   GCN CIRCULAR
NUMBER:  15482
SUBJECT: GRB 131108A: Continued RATIR Optical and NIR Observations
DATE:    13/11/11 18:15:07 GMT
FROM:    Eleonora Troja at GSFC  <eleonora.troja@nasa.gov>

Eleonora Troja (GSFC), 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), 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 131108A (Racusin et al., GCN 15464,
Vianello et al., GCN 15472 ) 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 2013/11
11.40 to 2013/11 11.53 UTC (61.01 to 64.03 hours after the LAT trigger),
obtaining a total of 2.04 hours exposure in the r and i bands and
0.89 hours exposure in the Z, Y, J, and H bands.

We continue to detect the previously reported source (Troja et al.,
GCN 15475).  In comparison with the SDSS DR9 and 2MASS, we obtain
the following detections and upper limits (3-sigma):

   r    22.4 ± 0.12
   i    22.03 ± 0.11
   Z   21.95 ± 0.22
   Y   21.6 ± 0.3
   J    > 21.5
   H   > 21.0

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. A comparison with our earlier
observations suggests a decay index of approximately -1.6 between our
observations of 2013 Nov 9 and these observations.

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