TITLE:   GCN CIRCULAR
NUMBER:  14431
SUBJECT: GRB 130420A: Continued RATIR Optical and NIR Observations
DATE:    13/04/21 16:54:47 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>

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 again observed the field of GRB 130420A (Page et al., GCN 14406) 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 21.30 to 2013/04 21.47UTC (23.66 to 27.79 hours after the BAT trigger), obtaining a total of 1.44 hours exposure in the r' and i' bands and 0.59 hours exposure in the Z, Y, J, and H bands.

The afterglow is well-detected.  In comparison with SDSS DR8 and 2MASS, we obtain:

 r'   22.11 +/- 0.08
 i'   21.90 +/- 0.09
 Z   21.52 +/- 0.18
 Y   21.40 +/- 0.31
 J   21.24 +/- 0.26
 H   20.38 +/- 0.23

These magnitudes are in the AB system, quoted with 1-sigma uncertainty, and not corrected for Galactic extinction in the direction of the GRB.  In comparison with our observations on the previous night (Watson et al., GCN 14409), the afterglow has faded by more than about 2 magnitudes in all bands.

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