TITLE:   GCN CIRCULAR
NUMBER:  15978
SUBJECT: GRB 140311A: RATIR Optical and NIR Detection
DATE:    14/03/13 00:11:31 GMT
FROM:    Owen Littlejohns at Az State U  <olittlej@asu.edu>

Owen Littlejohns (ASU), 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), 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 140311A (Racusin, et al., GCN 15944) 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 2014/03 12.24 to 2014/03 12.36
UTC (8.75 to 11.51 hours after the BAT trigger), obtaining a total of
2.10 hours exposure in the r and i bands and 0.89 hours exposure in the
Z and Y bands.

For a source within the Swift-XRT error circle (Evans, et al., GCN
15959), in comparison with the SDSS DR9 and 2MASS, we obtain the
following detections:

  r     22.33 +/- 0.13
  i     21.56 +/- 0.08
  Z     20.58 +/- 0.08
  Y     20.09 +/- 0.08

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. The source has faded in comparison
to observations from other facilities (D'Avanzo et, al., GCN 15953),
requiring a power-law with a temporal decay index of alpha = -0.83.

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