[vsnet-grb-info 13928] GRB 130831A: RATIR Confirmation of NIR/Optical Afterglow Flattening

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15242
SUBJECT: GRB 130831A: RATIR Confirmation of NIR/Optical Afterglow Flattening
DATE:    13/09/22 15:05:22 GMT
FROM:    Nat Butler at Az State U  <natbutler at asu.edu>

William H. Lee (UNAM), Alan M. Watson (UNAM), Nat Butler (ASU), 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),
José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM),
Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC)
report:

We again 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 Astronómico Nacional
on Sierra San Pedro Mártir from 2013/09 22.11 to 2013/09 22.31 UTC (21.57
to 21.77 days after the BAT trigger), obtaining a total of 6.40 hours
exposure in the r and i bands and 2.60 hours exposure in the Z, Y, J, and H
bands.

For a source within the Swift-XRT error circle (Evans et al., GCN 15147),
in comparison with SDSS DR9 and 2MASS, we obtain the following detections
and upper limits (3-sigma):

  r     23.02 +/- 0.14
  i     22.78 +/- 0.13
  Z     > 22.87
  Y     > 22.35
  J     21.62 +/- 0.19
  H     > 21.75

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  The flux levels are consistent
with our prior upper limits measured 4 days after the GRB (Butler et al.,
GCN 15179) and with the measurements reported by Pozanenko et al. (GCN
15237), confirming a flattening of the afterglow light curve.

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