TITLE:   GCN CIRCULAR
NUMBER:  14388
SUBJECT: GRB 130418A: RATIR Optical and NIR Observations
DATE:    13/04/19 05:30:29 GMT
FROM:    Nat Butler at UC berkeley  <natxbutler@gmail.com>

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 130418A (De Pasquale, et al., GCN 14377) 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 2013/04 19.14 to 2013/04 19.19 UTC (8.24 to
9.54 hours after the BAT trigger), obtaining a total of 1.07 hours exposure
in the r' and i' bands and 0.45 hours exposure in the Z, Y, J, and H bands.

For a source within the Swift-UVOT error circle (Kuin et al., GCN 14384),
in comparison with SDSS DR8 and 2MASS, we obtain the following detections
in the AB magnitude system:

 r'    18.87 +/- 0.02
 i'    18.77 +/- 0.02
 Z    18.30 +/- 0.02
 Y    18.07 +/- 0.02
 J    18.06 +/- 0.02
 H    17.53 +/- 0.02

These magnitudes are not corrected for Galactic extinction in the direction
of the GRB.  Relative to the GROND detections about 3 hrs earlier (Nardini
et al., GCN 14386), the afterglow has faded by about 0.4 mag in all
optical/NIR bands.  Continued observations are planned.

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