TITLE:   GCN CIRCULAR
NUMBER:  21968
SUBJECT: GRB 171004A: RATIR Optical and NIR Observations 
DATE:    17/10/04 13:26:20 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@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 (U. Wash.), and Vicki
Toy (UMD) report:

We observed the field of GRB 171004A (Cenko et al., GCN Circ. 21966)
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 4.45 to
2017/10 4.45 to 2017/10 4.52 UTC (2.97 to 4.45 hours after the BAT
trigger), obtaining a total of 1.07 hours exposure in the r and i bands
and 0.45 hours exposure in the Z, Y, J, and H bands.

We detect two sources within the Swift-XRT error circle. One is a
cataloged SDSS source. The other is at 09:16:40.66 +52:41:30.4 (J2000
+/- 0.5 arcsec) and, in comparison with the SDSS DR9 and 2MASS catalogs,
has

  r	= 21.91 +/- 0.11
  i	= 21.32 +/- 0.07
  Z	= 21.13 +/- 0.15
  Y	= 20.43 +/- 0.12
  J	= 20.45 +/- 0.15
  H	= 19.88 +/- 0.13

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

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