William H. Lee (UNAM), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), Michael G. Richer (UNAM), Chris Klein (UCB),
Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino
Cucchiara (UCSC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), 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 130831A (Hagen, et al., GCN 15139) 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 2013/10 9.10 to 2013/10 9.47 UTC (925.41
to 934.19 hours after the BAT trigger), obtaining a total of 6.08 hours
exposure in the r and i bands and 2.61 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 > 24.14
i > 23.63
Z > 22.94
Y > 22.45
J > 22.23
H > 21.74
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.
As compared with our previous RATIR observations (Lee et al., GCN 15274) we
confirm the fading in r and i by at least 0.3 and 0.4 and magnitudes, respectively.
The upper limits in Z, Y, J, and H are also consistent with fading.
Overall our measurements (Butler et al. GCN 15165, Watson et al. GCN 15179,
Lee et al., GCN 15242, 15274) are consistent with the re-brightening due to
a SN, as reported by Pozanenko et al. (GCN 15237) and spectroscopically by
Klose et al. (GCN 15320), and fading.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro