{
  "bibcode": "2018GCN.23017....1W",
  "body": "Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), William\nH. Lee (UNAM), Carlos Rom��n-Z����iga (UNAM), Alexander Kutyrev (GSFC), and\nEleonora Troja (GSFC) report:\n\nWe observed the field of GRB 180720B (Siegel et al., GCN Circ. 22973)\nwith the COATLI 50-cm telescope and interim imager at the Observatorio\nAstron��mico Nacional on the Sierra de San Pedro M��rtir\n(http://coatli.astroscu.unam.mx) from 2018-07-22 06:25 to 11:23 UTC\n(from 40.07 to 45.03 hours after the trigger), obtaining a total of 4.06\nhours of exposure in the w filter.\n\nWe detect the optical counterpart (Martone et al., GCN Circ. 22976) with\n\nw = 20.07 +/- 0.02\n\nThese magnitudes are calibrated against the USNO-B1 catalog (adjusted to\nan approximate AB system) and are not corrected for Galactic extinction\nin the direction of the GRB.\n\nWe thank the COATLI technical team (Fernando ��ngeles, Oscar Chapa,\nSalvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosal��a Langarica,\nFernando Quir��s, and Carlos Tejada) and the staff of the Observatorio\nAstron��mico Nacional.",
  "circularId": 23017,
  "createdOn": 1532292729000,
  "email": "alan@astro.unam.mx",
  "subject": "GRB 180720B: COATLI Optical Detection",
  "submitter": "Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>",
  "eventId": "GRB 180720B"
}