[vsnet-grb-info 19561] GRB 170705A: Further RATIR Optical and NIR Observations and Steepening of Fading

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21303
SUBJECT: GRB 170705A: Further RATIR Optical and NIR Observations and Steepening of Fading 
DATE:    17/07/06 18:37:15 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan at astro.unam.mx>

Alan M. Watson (UNAM), Nat Butler (ASU), 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 Circ. 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 6.17 to 2017/07 6.26 UTC (25.33
to 27.52 hours after the BAT trigger), obtaining a total of 1.02 hours
exposure in the r and i bands and 0.37 hours exposure in the Z,
Y, J, and H bands.

For a source within the Swift-XRT error circle, in comparison with the SDSS DR9 and 2MASS catalogs, we obtain the following detections:

 r	= 20.62 +/- 0.05
 i	= 20.35 +/- 0.05
 Z	= 19.68 +/- 0.07
 Y	= 19.72 +/- 0.09
 J	= 19.46 +/- 0.10
 H	= 19.61 +/- 0.16

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

The source has faded on average by 1.90 +/- 0.17 magnitudes compared to our previous observations (Butler et al., GCN Circ. 21293). This corresponds to a temporal index of -0.72 +/- 0.03, which is steeper than the index of -0.4 we saw during our previous observations.

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