[vsnet-grb-info 19955] GRB 171020A: Continued RATIR Optical and NIR Observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22042
SUBJECT: GRB 171020A: Continued RATIR Optical and NIR Observation
DATE:    17/10/22 21:19:00 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 observed the field of GRB 171020A (Page, et al., GCN 22028) 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 22.13 to 2017/10 22.47 UTC (27.94 to
36.23 hours after the BAT trigger), obtaining a total of 5.27 hours
exposure in the r and i bands and 2.21 hours exposure in the Z and Y bands.

We contine to detect the optical transient (Malesani, et al., GCN 22029;
also, Moskvitin, et al., GCN 22031; Butler, et al., GCN 22037).  In
comparison with the USNO-B1 and 2MASS catalogs, we obtain the following
detections and upper limits (3-sigma):

 r = 23.25 +/- 0.14
 i = 23.01 +/- 0.11
 Z > 21.75
 Y > 22.05

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  Compared to our observations last
night, these data suggest either a slow afterglow fade (~t^-0.2) or that
our measured flux contains flux from the GRB host galaxy.

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