TITLE:   GCN CIRCULAR
NUMBER:  15359
SUBJECT: GRB 131018A: RATIR Optical and NIR Observations
DATE:    13/10/19 18:51:08 GMT
FROM:    Nat Butler at Az State U  <natbutler@asu.edu>

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 131018A (Melandri, et al., GCN 15349) 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 19.34 to 2013/10 19.53 UTC (19.36 to
23.83 hours after the BAT trigger), obtaining a total of 2.58 hours
exposure in the r and i bands and 1.09 hours exposure in the Z, Y, J, and H
bands.

We detect no new sources within the enhanced Swift-XRT error circle (Goad,
et al., GCN 15352).  In comparison with the SDSS DR9 and 2MASS, we obtain
the following upper limits (3-sigma):

  r > 23.30
  i > 23.18
  Z > 22.43
  Y > 22.05
  J > 21.70
  H > 21.27

The SDSS source present in the XRT error circle (see also, Zheng, et al.,
GCN 15355) is well-detected, apparently non-extended, and is measured to
have the following magnitudes:

  r     22.06 +/- 0.11
  i     20.73 +/- 0.05
  Z     20.10 +/- 0.05
  Y     19.63 +/- 0.05
  J     19.64 +/- 0.06
  H     19.18 +/- 0.06

The above magnitude are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

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