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), Jos� A. de Diego (UNAM), Leonid Georgiev (UNAM),
Jes�s Gonz�lez (UNAM), Carlos Rom�n-Z��iga (UNAM), Neil Gehrels (GSFC),
and Harvey Moseley (GSFC) report:
We have been monitoring GRB 130427A with the Reionization and
Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold
Johnson Telescope at the Observatorio Astron�mico Nacional on Sierra San
Pedro M�rtir. We have precise and homogeneous photometry for all nights
except 2013 May 6.
During the first night the optical afterglow is well-fitted by a power
law with an index of -1. However, around 1 day after the burst there is
a break, and the power law steepens.
Our photometry in gri from 2 to 11 days is well-fitted by a power law
with an index very close to -1.5 plus a constant contribution with i =
21.23 � 0.05, g-i = 0.74 � 0.12, and r-i = 0.05 � 0.05, consistent
with the SDSS DR9 photometry of the presumed host galaxy.
We see no evidence for an additional component such as the one mentioned
by Xu et al. (GCN Circular 14597).
Further observations are planned.
We thank the staff of the Observatorio Astron�mico Nacional in San Pedro