TITLE:   GCN CIRCULAR
NUMBER:  17595
SUBJECT: GRB 150317A: RATIR Optical Afterglow Detection
DATE:    15/03/17 14:41:50 GMT
FROM:    Nat Butler at Az State U  <natbutler@asu.edu>

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 150317A (Siegel, et al., GCN 17592) 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 2015/03 17.18 to 2015/03 17.43 UTC (3 minutes
to 5.9 hours after the BAT trigger), obtaining a total of 3 hours exposure
in the r, i, and z bands.

We find an uncatalogued source within the Swift-XRT error circle (Evans et
al., GCN 17594).  In comparison with the SDSS DR9 and 2MASS, we obtain the
following detections and upper limit (3-sigma):

  r     20.5 +/- 0.1
  i     21.7 +/- 0.1
  z     > 20.8

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  This photometry is preliminary and
can be expected to improve with a more detailed analysis due to the
proximity of a bright star (e.g., Xu, et al., GCN 17593).

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