[vsnet-grb-info 19849] GRB 170921A: RATIR Optical Afterglow Detection and NIR Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21915
SUBJECT: GRB 170921A: RATIR Optical Afterglow Detection and NIR Observations
DATE:    17/09/22 23:22:09 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 (ASU), and Vicki Toy (UMD) report:

We observed the field of GRB 170921A (D'Ai, et al., GCN 21901) 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 2017/09 22.18 to 2017/09 22.51 UTC (13.82 to
21.76 hours after the BAT trigger), obtaining a total of 5.29 hours
exposure in the r and i bands and 2.22 hours exposure in the Z, Y, J, and H
bands.

For a source within the Swift-XRT error circle (Beardmore, et al., GCN
21906), in comparison with the SDSS DR9 and 2MASS catalogs, we obtain the
following weak detections and upper limits (3-sigma):

  r = 24.45 +/- 0.34
  i = 24.38 +/- 0.34
  Z > 23.05
  Y > 22.83
  J > 22.47
  H > 22.19

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.