{
  "bibcode": "2017GCN.21389....1W",
  "body": "Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), Carlos\nRom��n-Z����iga (UNAM), and William H. Lee (UNAM) report:\n\nWe observed the field of the short GRB 170728B (Cenko et al., GCN Circ.\n21371) with the COATLI 50-cm telescope and interim imager (Watson et al.\n2016, Proc. SPIE, 9908, 50) at the Observatorio Astron��mico Nacional on\nthe Sierra de San Pedro M��rtir from 2017-07-29 04:21 to 08:19 obtaining\na total of 2.76 hours of observation in the clear filter.\n\nWe detect the source reported by D���Avanzo et al. (GCN Circ. 21372).\nCalibrating with respect to the USNO-B1 catalog, we estimate a\npreliminary magnitude of\n\nR = 22.40 +/- 0.16.\n\nThis magnitude is in the USNO-B1 Vega system and is corrected for\nGalactic extinction in the direction of the GRB.\n\nThe source has faded by around two magnitudes between the observations\nin the first hour or so (D���Avanzo et al., GCN Circ. 21372; Heintz et al,\nGCN Circ. 21374; and Guidorzi et al., GCN Circ. 21375) and our\nobservations. This confirms that the source is the optical transient\nassociated with 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": 21389,
  "createdOn": 1501381258000,
  "email": "alan@astro.unam.mx",
  "subject": "GRB 170728B: COATLI Observations And Confirmation of Fading",
  "submitter": "Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>",
  "eventId": "GRB 170728B"
}