[vsnet-grb-info 13102] GRB 130420A: Continued RATIR Optical and NIR Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14439
SUBJECT: GRB 130420A: Continued RATIR Optical and NIR Observations
DATE:    13/04/22 21:22:43 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan at astro.unam.mx>

Alan M. Watson (UNAM), Nat Butler (ASU), 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 Circular
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 22.35 to
2013/04 22.47 UTC (48.84 to 51.69 hours after the BAT trigger),
obtaining a total of 0.71 hours exposure in the r' and i' bands and 0.29
hours exposure in the Z, Y, J, and H bands.

The afterglow is again detected in several bands.  In comparison with
SDSS DR8 and 2MASS, we obtain:

r' 22.63 +/- 0.17
i' 22.46 +/- 0.17
Z  21.62 +/- 0.25
Y > 21.32
J > 21.39
H > 20.91

These magnitudes are in the AB system, quoted with 1-sigma uncertainty,
and not corrected for Galactic extinction in the direction of the GRB. 
The upper limits are at the 3-sigma level.

In comparison with our earlier observations (Watson et al., GCN Circular
14409; Butler et al., GCN Circular 14431), we see that the afterglow
faded by about 2 magnitudes from about 3 to about 25 hours after the
Swift trigger, but then by only about another 0.5 magnitudes from about
25 to about 50 hours after the Swift trigger.

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