TITLE:   GCN CIRCULAR
NUMBER:  15475
SUBJECT: GRB 131108A: RATIR Optical and NIR Observations
DATE:    13/11/09 16:32:22 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 the LAT 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
9.41 to 2013/11 9.53 UTC (13.06 to 16.11 hours after the LAT trigger),
obtaining a total of 2.11 hours exposure in the r and i bands and 0.76 
hours
exposure in the Z, Y, J, and H bands.

For a source within the enhanced XRT error circle (Stroh & Kennea, GCN
15474) , in comparison with the SDSS DR9 and 2MASS, we obtain the
following detections:

   r    19.91 ± 0.02
   i    19.70 ± 0.02
   Z    19.57 ± 0.04
   Y    19.23 ± 0.05
   J    19.34 ± 0.07
   H    19.09 ± 0.08

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. We can confirm that this source 
fades
during our observations with a power-law decay index of approximately -2.

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