[vsnet-grb-info 16851] GRB 150811A: Continued RATIR Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18132
SUBJECT: GRB 150811A: Continued RATIR Observations
DATE:    15/08/12 18:18:04 GMT
FROM:    Nat Butler at UC berkeley  <natxbutler at gmail.com>

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), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús
González (UNAM), Carlos Román-Zúñiga (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 Astronómico Nacional on
Sierra San Pedro Mártir 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
  z >18.9

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 Astronómico Nacional in San Pedro
Mártir.  Further observations are planned.