TITLE:   GCN CIRCULAR
NUMBER:  22934
SUBJECT: GRB 180709A: COATLI Optical Observations
DATE:    18/07/09 15:27:42 GMT
FROM:    Nat Butler at Az State U  <natbutler@asu.edu>

Nat Butler (ASU), Alan M. Watson (UNAM), aRosa 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 180709A (Marshall et al., GCN Circ 22930) 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 2018-07-09 10:53:05.6 to 11:26:07.1
UTC (from 65.4 seconds after the trigger or 14.5 seconds after the alert to
0.55 hours after the trigger), obtaining a total of 695 seconds of exposure
in the w filter.

For a source within the XRT error region (Marshall et al., GCN Circ.
22930), we determine a 3-sigma upper limit of

 w > 21.3

This magnitude is calibrated against the USNO-B1 catalog (adjusted to an
approximate AB system) and is not corrected for Galactic extinction in the
direction of the GRB.

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.