TITLE:   GCN CIRCULAR
NUMBER:  23094
SUBJECT: GRB 180806A/180806.94: Refined COATLI Photometry of MASTER OT J004613.05+242014.1 
DATE:    18/08/07 16:02:35 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>

Nat Butler (ASU), Alan M. Watson (UNAM), Rosa L. Becerra (UNAM), William
H. Lee (UNAM), Carlos Román-Zúñiga (UNAM), Alexander Kutyrev (GSFC), and
Eleonora Troja (GSFC) report:

We observed the field of the MASTER OT J004613.05+242014.1 (Lipunov et
al., GCN Circ. 23091), possibly associated with GRB 180806A/180806.94
(Fermi trigger 555287944), with the COATLI 50-cm telescope and interim
imager at the Observatorio Astronómico Nacional on the Sierra de San
Pedro Mártir (http://coatli.astroscu.unam.mx) from 2018-08-07 11:23:26
UTC to 12:21:39 UTC (12.74 to 13.71 hours after trigger), obtaining a
total of 2730 seconds of exposure in the w filter.

We detect a source coincident with the reported coordinates of the OT
(Lipunov et al., GCN Circ. 23091) with

w = 20.22 +/- 0.05

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.

This photometry supersedes that reported by Watson et al. (GCN 23092).

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.