TITLE:   GCN CIRCULAR
NUMBER:  20915
SUBJECT: GRB 170318A: RATIR Optical and NIR Observations
DATE:    17/03/18 22:08:37 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), Ori Fox (STScI), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora
Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jesús
González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey Moseley (GSFC), John
Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:

We observed the field of GRB 170318A (Sbarufatti, et al., GCN 20904) 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 2017/03 18.51 to 2017/03 18.53 UTC (3.0 to
27.6 minutes after the BAT trigger), obtaining a total of 0.24 hours
exposure in the r and i bands and 0.11 hours exposure in the Z, Y, J, and H
bands.

We do not detect a source within the Swift-XRT error circle (Evans, et al.,
GCN 20907).  In comparison with the USNO-B1 and 2MASS catalogs, we obtain
the following upper limits (3-sigma):

 r > 23.39
 i > 22.82
 Z > 21.72
 Y > 21.56
 J > 21.12
 H > 20.73

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  We note that this field suffers
large Galactic extinction (A_V~3).

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