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GCN Circular 19663

GRB 160705B: RATIR Optical and NIR Observations and Confirmation of the Fading Afterglow
2016-07-06T13:50:49Z (8 years ago)
Alan M. Watson at Instituto de Astronomia UNAM <>
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
(GSFC/STScI), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico
Ramirez-Ruiz (UCSC), Jos�� A. de Diego (UNAM), Leonid Georgiev (UNAM),
Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (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 160705B (Cannizzo et al., GCN 19657) with
the Reionization and Transients Infrared Camera (RATIR;
on the 1.5m Harold Johnson Telescope at the Observatorio Astron��mico
Nacional on Sierra San Pedro M��rtir from 2016/07 6.17 to 2016/07 6.21
UTC (7.04 to 8.05 hours after the BAT trigger), obtaining a total of
0.66 hours exposure in the r and i bands and 0.30 hours exposure in the
Z, Y, J, and H bands.

We detect two sources within the enhanced Swift-XRT error circle
(Osborne et al., GCN 19659). The brighter source is an uncataloged source
at 11:12:26.20 +46:42:01.2 (J2000, +/- 0.5 arcsec) with the following
detections and 3-sigma upper limit:

r = 22.89 +/- 0.15
i = 22.12 +/- 0.09
Z = 22.34 +/- 0.33
Y = 21.73 +/- 0.32
J > 21.54
H = 20.98 +/- 0.34

The fainter source is a cataloged SDSS source at 11:12:26.42 +46:41:59.6
(J2000, +/- 0.5 arcsec) with the following detections and 3-sigma upper

r = 23.39 +/- 0.24
i = 22.61 +/- 0.14
Z = 22.10 +/- 0.26
Y > 21.87
J > 21.54
H > 21.04

These magnitudes are in the AB system, are in comparison with the SDSS
DR9 and 2MASS catalogs, and are not corrected for Galactic extinction in
the direction of the GRB.

We note that Guidorzi et al. (GCN 19658) report an uncataloged source
with r of about 21 at 36 minutes after the burst trigger. Their source
is only 0.7 arcsec from our brighter uncataloged source and so we
postulate that these correspond to the afterglow of the GRB. The
afterglow has faded by about 2 magnitudes between their observations at
36 minutes and ours at 7.54 hours, which corresponds to a temporal index
of about -0.6.

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
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