TITLE:   GCN CIRCULAR
NUMBER:  20609
SUBJECT: GRB 170205A: RATIR Optical and NIR Observations
DATE:    17/02/05 19:35:56 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), Neil Gehrels (GSFC), Harvey
Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy
(UMD) report:

We observed the field of GRB 170205A (Troja, et al., GCN 20603) 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 2017/02 5.53 to 2017/02 5.58 UTC (2.3 minutes
to 1.25 hours after the BAT trigger), obtaining a total of 0.61 hours
exposure in the r and i bands and 0.29 hours exposure in the Z and Y bands.

In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following
detections for the optical afterglow (see, also, Guidorzi, et al., GCN
20605):

r = 18.31 +/- 0.01
i = 17.90 +/- 0.01
Z = 18.06 +/- 0.01
Y = 19.26 +/- 0.07

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  The source fades (from i~16 mag)
as t^(-1.6) until ~15 minutes after the GRB, after which the fade flattens
to t^(-1.1).

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