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
(ORAU/GSFC), 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 observed the field of GRB 150811A (Evans, et al., GCN 18119) 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 from 2015/08 12.15 to 2015/08 12.41 UTC (23.39 to
29.66 hours after the BAT trigger), obtaining a total of 4.98 hours
exposure in the r, i, and z bands.
We continue to detect the source we reported earlier (Butler, et al.; GCN
18120), which we also observed for several additional hours on the first
night. In comparison with the USNO-B1 and 2MASS catalogs, we obtain the
following detections and upper limit (3-sigma):
r 21.68 +/- 0.14
i 21.48 +/- 0.05
These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. In comparison with our previous
observations, the source flux has declined approximately as t^(-1).
We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir. Further observations are planned.