[vsnet-grb-info 19974] GRB 171027A: RATIR Confirmation of Fading and Photo-z

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22061
SUBJECT: GRB 171027A: RATIR Confirmation of Fading and Photo-z
DATE:    17/10/27 14:50:03 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 (U. Wash.), and Vicki Toy (UMD) report:

We continued to observe the field of GRB 171027A (D'Avanzo et al., et al.,
GCN 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 27.53 UTC (0.04 to 4.24 hours after the BAT trigger), obtaining a
total of 2.82 hours exposure in the r and i bands and 1.18 hours exposure
in the Z, Y, J, and H bands.

At late time, the source is only detected in the H-band, with H = 19.12 +/-
0.06.  This magnitude is calibrated relative to 2MASS and is in the AB
system, not corrected for Galactic extinction in the direction of the GRB.
We measure a fade in the H-band flux in time as t^(-1.0+/-0.1).

Using all bands (see, Watson et al., GCN 22057), we find high A_V photo-z
solutions nearby (z<3.85, 90% conf.) and a high-z solution which assumes
A_V=0 (z=9+/-1).  We note that the XRT N_H constraints (D'Avanzo et al., et
al., GCN 22053) point toward the high A_V solution, although with low
statistical significance.

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