TITLE:   GCN CIRCULAR
NUMBER:  16937
SUBJECT: GRB 141004A: RATIR Late Time Optical and NIR Observations
DATE:    14/10/21 21:58:12 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 (ORAU/GSFC), Eleonora Troja
(GSFC), Enrico Ramirez-Ruiz (UCSC), Jos�� A. de Diego (UNAM), Leonid
Georgiev (UNAM), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM),
Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report:

We observed the field of GRB 141004A (D'Elia, et al., GCN 16878) with
the Reionization and Transients Infrared Camera (RATIR; www.ratir.org)
on the 1.5m Harold Johnson Telescope at the Observatorio Astron��mico
Nacional on Sierra San Pedro M��rtir from 2014/10 21.31 to 2014/10 21.51
UTC (392.08 to 396.95 hours after the BAT trigger), obtaining a total
of 3.89 hours exposure in the r, i and z bands.

We continue to detect the source reported from the previous epoch of
RATIR observations (Littlejohns, et al., GCN 16887). We obtain the
following detections and upper limit (3-sigma):

  r     24.21 +/- 0.24
  i     23.24 +/- 0.14
  z     > 21.47

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

These magnitudes suggest the source to remain brighter than expected if
determined purely from a typical GRB power-law decay. This may
corroborate the claim of re-brightening (Schulze, et al., GCN 16936),
however, it may also indicate the detection of the host galaxy (de Ugarte
Postigo, et al., GCN 16902). We also note that these magnitudes are
broadly consistent with those observed by GROND at an approximate epoch
of 32 hours after the initial Swift/BAT trigger (Schmidl, et al., GCN
16899).

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.