TITLE:   GCN CIRCULAR
NUMBER:  22057
SUBJECT: GRB 171027A: RATIR Detection of a NIR Afterglow Candidate 
DATE:    17/10/27 11:20:05 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>

Alan M. Watson (UNAM), Eleonora Troja (GSFC), 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), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz
(UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey
Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki
Toy (UMD) report:

We observed the field of GRB 171027A (D'Avanzo et al., GCN Circ. 22053)
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 2017/10 27.35 to
2017/10 27.37 UTC (0.04 to 0.51 hours after the BAT trigger), obtaining
a total of 0.36 hours exposure in the r and i bands and 0.15 hours
exposure in the Z, Y, J, and H bands.

For a source within the Swift-XRT error circle, in comparison with the
USNO-B1 and 2MASS catalogs, we obtain the following detections and upper
limits (3-sigma):

  r	> 23.17
  i	> 23.12
  Z	> 20.66
  Y	> 21.09
  J	= 20.95 +/- 0.26
  H	= 19.12 +/- 0.06

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB. The source position is at RA,
Dec (J2000) = 04:06:45.77 -02:37:18.9 (+/- 0.5 arcsec). We currently
have no evidence for fading.

The very red colors suggest that this might be at high redshift or
dusty.

Further observations are planned.

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