TITLE:   GCN CIRCULAR
NUMBER:  22954
SUBJECT: GRB 180715A: COATLI Optical Observations
DATE:    18/07/17 04:44:52 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 the short GRB 180715A (Ukwatta et al., GCN Circ.
22947) 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 2018-07-16 03:40:25 to 08:07:12 UTC
(9.55 to 14.00 hours after the trigger), obtaining a total of 3.33 hours
of exposure in the w filter.

We do not detect any optical sources coincident with the five X-ray
sources reported by Kennea et al. (GCN Circ. 22953) to a 5-sigma limiting
magnitude of

w > 22.4

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.