TITLE:   GCN CIRCULAR
NUMBER:  15312
SUBJECT: GRB 131004A: RATIR Optical and NIR Upper Limits
DATE:    13/10/05 15:33:25 GMT
FROM:    Owen Littlejohns at Az State U  <olittlej@asu.edu>

Owen Littlejohns (ASU), 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 (UCSC),
Eleonora Troja (GSFC), 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 131004A (Hagen, et al., GCN 15303) 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 2013/10 5.12 to 2013/10 5.30 UTC (5.12
to 9.44 hours after the BAT trigger), obtaining a total of 2.17 hours
exposure in the r and i bands and 0.94 hours exposure in the Z,
Y, J, and H bands.

For a source within the Swift-XRT error circle, in comparison with 2MASS, we
obtain the following upper limits (3-sigma):

  r     > 23.91
  i     > 23.33
  Z     > 22.56
  Y     > 21.86
  J     > 21.81
  H     > 21.26

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. We did not detect the source
reported in Xu et al. (GCN 15304). In comparison with earlier GROND
observations (Schmidl, et al., GCN 15309) the source has faded by a minimum
of 1.7 magnitudes in the r band. This implies a power-law decay steeper
than t^-1.7.

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