[vsnet-grb-info 19550] GRB 170705A: RATIR Optical and NIR Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21293
SUBJECT: GRB 170705A: RATIR Optical and NIR Observations
DATE:    17/07/05 14:58:02 GMT
FROM:    Nat Butler at Az State U  <natbutler at 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 170705A (Starling, et al., GCN 21289) 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 2017/07 5.17 to 2017/07 5.26 UTC (1.34 to 3.41
hours after the BAT trigger), obtaining a total of 1.42 hours exposure in
the r and i bands and 0.59 hours exposure in the Z, Y, J, and H bands.

We detect the optical transient found by Swift and observed MASTER-OAFA
(Lipunov, et al., GCN 21291).  In comparison with the SDSS DR9 and 2MASS
catalogs, we obtain the following detections:

 r = 18.60 +/- 0.01
 i = 18.30 +/- 0.01
 Z = 18.03 +/- 0.01
 Y = 17.79 +/- 0.01
 J = 17.79 +/- 0.01
 H = 17.56 +/- 0.01

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  The source fades as in time as
t^(-0.4) during our observation.

We note that the Swift-UVOT detection makes this GRB unlikely to be at very
high redshift.  Our photo-z calculations, using RATIR data alone, suggest
z<4.

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