TITLE:   GCN CIRCULAR
NUMBER:  22910
SUBJECT: GRB 180706A: COATLI Optical Detection 
DATE:    18/07/06 09:02:57 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), Carlos
Román-Zúñiga (UNAM), and William H. Lee (UNAM) report:

We observed the field of the GRB 180706A (Stamatikos et al., GCN Circ.
22909) with the COATLI 50-cm telescope and interim imager (Watson et al.
2016, Proc. SPIE, 9908, 50) at the Observatorio Astronómico Nacional on
the Sierra de San Pedro Mártir from 2018-07-06 08:25:26.83 (29.5 seconds
after alert and 46.4 seconds after trigger) to 08:50:34, obtaining 795
seconds of exposure in the w filter.

We detect an uncatalogued source in the XRT error region with a
preliminary magnitude of

  w = 18.73 +/- 0.08

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.

At the moment we have no information on fading. Further observations are
planned.

We thank the COATLI technical team (Fernando Ángeles, Oscar Chapa,
Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosalía Langarica,
Fernando Quirós, and Carlos Tejada) and the staff of the Observatorio
Astronómico Nacional.