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GCN Circular 15274

GRB 130831A: Continued RATIR Optical and NIR Observations
2013-09-30T16:17:13Z (11 years ago)
Nat Butler at Az State U <>
William H. Lee (UNAM), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), Nat
Butler (ASU), 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)

We observed the field of GRB 130831A (Hagen, et al., GCN 15139) with the
Reionization and Transients Infrared Camera (RATIR; on the
1.5m Harold Johnson Telescope at the Observatorio Astron�mico Nacional on
Sierra San Pedro M�rtir from 2013/09 30.12 to 2013/09 30.49 UTC (29.58 to
29.94 days after the BAT trigger), obtaining a total of 6.27 hours exposure
in the r and i bands and 2.65 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 2MASS, we obtain the following detections and upper
limits (3-sigma):

  r     23.84 +/- 0.18
  i     23.23 +/- 0.15
  Z     > 23.04
  Y     > 22.53
  J     > 22.37
  H     > 21.72

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  The source has faded relative to
our last measurement (t~21.5 days; Lee et al., GCN 15242) by about 0.8
magnitudes in r and J and 0.5 magnitudes in i.  Our measurements (see,
also, Watson et al., GCN 15179; Butler et al., GCN 15165) are consistent
with a bump or re-brightening in the lightcurve at t~10 days (see,
Pozanenko et al., GCN 15237), followed by continued fading.

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