TITLE:   GCN CIRCULAR
NUMBER:  18141
SUBJECT: GRB 150811A: Continued RATIR Observations
DATE:    15/08/14 20:01:44 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), 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), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) 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 14.22 to 2015/08 14.41 UTC (73.12 to
77.68 hours after the BAT trigger), obtaining a total of 3.56 hours
exposure in the r, i, and z bands.

In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following
detections and upper limit (3-sigma):

  r = 22.4 +/- 0.3
  i = 22.0 +/- 0.4
  z > 20.37

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  The fading of the source remains
consistent with t^(-1) (see, Butler et al., 18120, 18132, 18140).

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.