TITLE:   GCN CIRCULAR
NUMBER:  22806
SUBJECT: GRB 180620A: COATLI Detection and Light Curve
DATE:    18/06/20 15:16:55 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>

Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), William
H. Lee (UNAM), Carlos Rom��n-Z����iga (UNAM), Alexander Kutyrev (GSFC), and
Eleonora Troja (GSFC) report:

We observed the field of GRB 180620A (Evans et al., GCN 22798) with the
COATLI 50-cm telescope and interim imager at the Observatorio
Astron��mico Nacional on the Sierra de San Pedro M��rtir
(http://coatli.astroscu.unam.mx) from 2018-06-20 08:35:37 to 11:17:31
(from 39.2 seconds after the trigger or 21.1 seconds after the alert to
2.7 hours after the trigger), obtaining a total of 6250 seconds of
exposure in the w filter.

We detect the source reported by Butler et al. (GCN Circ. 22799) with

w = 18.00 +/- 0.02

This magnitude is in the USNO system and is not corrected for Galactic
extinction in the direction of the GRB.

Our light curve shows a sharp initial fall from 16.5 mag to 17.3 mag,
followed by a slower rise to 16.7 mag (also seen by Butler et al.),
followed by a monotonic fall to 19.0 mag.

We thank the COATLI technical team (Fernando ��ngeles, Oscar Chapa,
Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosal��a Langarica,
Fernando Quir��s, and Carlos Tejada) and the staff of the Observatorio
Astron��mico Nacional.