TITLE:   GCN CIRCULAR
NUMBER:  14679
SUBJECT: GRB 130518A: RATIR Optical and NIR Observations
DATE:    13/05/19 17:59:08 GMT
FROM:    Eleonora Troja at GSFC  <eleonora.troja@nasa.gov>

Eleonora Troja (GSFC), 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), 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 130518A (Xiong, et al., GCN 14674; Omodei,
et al., GCN 14675) 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
from 2013/05 19.44 to 2013/05 19.47 UTC (20.54 to 21.49 hours after
the GBM trigger), obtaining a total of 0.64 hours exposure in the r'
and i' bands, 0.27 hours exposure in the Z and Y bands, and 0.15 hours
exposure in the J, and H bands.

We detect a new, uncatalogued source at RA,Dec = 355.66781, +47.46493
(J2000) with an uncertainty of 0.5 arcsec.
This position is 5 arcsec from the XRT localization, just outside the
XRT error circle (Evans, et al., GCN 14678). In comparison with SDSS DR8
and 2MASS, we obtain the following detections:

     r'    19.38 ± 0.02
     i'    19.10 ± 0.02
     Z     18.83 ± 0.04
     Y     18.65 ± 0.04
     J     18.28 ± 0.07
     H     18.47 ± 0.11

These magnitudes are in the AB system and not corrected for Galactic
extinction in the direction of the GRB. We have evidence at the 2-3 sigma
level of fading in r' and i' over the duration of our observations.

Further observations are planned.

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