{
  "bibcode": "2017GCN.21915....1B",
  "body": "Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William\nH. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier\nProchaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora\nTroja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jes��s\nGonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey Moseley (GSFC), John\nCapone (UMD), V. Zach Golkhou (ASU), and Vicki Toy (UMD) report:\n\nWe observed the field of GRB 170921A (D'Ai, et al., GCN 21901) with the\nReionization and Transients Infrared Camera (RATIR; www.ratir.org) on the\n1.5m Harold Johnson Telescope at the Observatorio Astron��mico Nacional on\nSierra San Pedro M��rtir from 2017/09 22.18 to 2017/09 22.51 UTC (13.82 to\n21.76 hours after the BAT trigger), obtaining a total of 5.29 hours\nexposure in the r and i bands and 2.22 hours exposure in the Z, Y, J, and H\nbands.\n\nFor a source within the Swift-XRT error circle (Beardmore, et al., GCN\n21906), in comparison with the SDSS DR9 and 2MASS catalogs, we obtain the\nfollowing weak detections and upper limits (3-sigma):\n\n  r = 24.45 +/- 0.34\n  i = 24.38 +/- 0.34\n  Z > 23.05\n  Y > 22.83\n  J > 22.47\n  H > 22.19\n\nThese magnitudes are in the AB system and are not corrected for Galactic\nextinction in the direction of the GRB.\n\nWe thank the staff of the Observatorio Astron��mico Nacional in San Pedro\nM��rtir.",
  "circularId": 21915,
  "createdOn": 1506122529000,
  "email": "natbutler@asu.edu",
  "subject": "GRB 170921A: RATIR Optical Afterglow Detection and NIR Observations",
  "submitter": "Nat Butler at Az State U  <natbutler@asu.edu>",
  "eventId": "GRB 170921A"
}