TITLE:   GCN CIRCULAR
NUMBER:  15223
SUBJECT: GRB 130907A: Continued RATIR Optical and NIR Observations
DATE:    13/09/13 04:41:50 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 (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 observed the field of GRB 130907A (Page et al., GCN 15183) 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 13.13 to 2013/09 13.16 UTC (125.49 to
126.24 hours after the BAT trigger), obtaining a total of 0.36 hours
exposure in the r and i bands and 0.15 hours exposure in the Z, Y, J, and H
bands.

For the source reported in Lee et al. (GCN 15192), in comparison with SDSS
DR9 and 2MASS, we obtain the following upper limits (3-sigma) in the AB
magnitude system (not corrected for Galactic extinction in the direction of
the GRB) :

  r     > 22.68
  i     > 22.62
  Z     > 21.30
  Y     > 20.70
  J     > 20.42
  H     > 19.69

We conclude from our most constraining limit (i-band), that the source has
faded by at least 0.9 mags since our observation 2 nights ago (Butler et
al., GCN 15209).  These magnitudes are now significantly fainter than the
DR9 catalog magnitudes of SDSS galaxy mentioned by Lee et al.

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