{
  "bibcode": "2018GCN.22846....1W",
  "body": "Alan M. Watson (UNAM), Eleonora Troja (GSFC), Nat Butler (ASU),\nAlexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer\n(UNAM), Ori Fox (STScI), J. Xavier Prochaska (UCSC), Josh Bloom (UCB),\nAntonino Cucchiara (UVI), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz\n(UCSC), Jes��s Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Harvey\nMoseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki\nToy (UMD) report:\n\nWe observed the field of GRB 180624A (Gibson et al., GCN Circ. 22832)\nwith the Reionization and Transients Infrared Camera (RATIR;\nwww.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio\nAstron��mico Nacional on Sierra San Pedro M��rtir from 2018/06 25.26 to\n2018/06 25.47 UTC (16.42 to 21.45 hours after the BAT trigger),\nobtaining a total of 3.91 hours exposure in the r and i bands.\n\nWe detect a source in the enhanced Swift-XRT error circle (Goad et al.,\nGCN Circ. 22835) with the following magnitudes:\n\n  r\t= 21.03 +/- 0.02\n  i\t= 20.45 +/- 0.01\n\nThese magnitudes are calibrated against the SDSS DR9 catalog, are in the\nAB system, and are not corrected for Galactic extinction in the\ndirection of the GRB.\n\nWe note that the source has faded significantly from the earlier\nobservations of Guidorzi et al. (GCN Circ. 22839) of r = 19.9 +/- 0.1 at\n0.54 hours and Schady (GCN Circ. 22840) of r = 20.2 +/- 0.1 at 15.07\nhours. We also see the source fade by about 0.5 mag in each our bands\nduring the course of our observations.\n\nWe confirm the observation of Rossi et al. (GCN Circ. 22845) that the\nsource is a couple of arcsec to the SE of the SDSS galaxy\nJ211223.25-022015.9.\n\nWe thank the staff of the Observatorio Astron��mico Nacional in San Pedro\nM��rtir.",
  "circularId": 22846,
  "createdOn": 1529964974000,
  "email": "alan@astro.unam.mx",
  "subject": "GRB 180624A: RATIR Optical Observations",
  "submitter": "Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>",
  "eventId": "GRB 180624A"
}