[vsnet-grb-info 20994] GRB 180806.94: COATLI Detection of MASTER OT J004613.05+242014.1 and Confirmation of Fading

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23092
SUBJECT: GRB 180806.94: COATLI Detection of MASTER OT J004613.05+242014.1 and Confirmation of Fading
DATE:    18/08/07 12:11:36 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan at astro.unam.mx>

Alan M. Watson (UNAM), Nat Butler (ASU), 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 OT MASTER OT J004613.05+242014.1 (Lipunov
et al., GCN Circ. 23091) possibly associated with GRB 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
11:52:11 UTC, obtaining a total of 1440 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), and preliminary photometry suggests

w = 20.0 +/- 0.2

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.

Our observations would appear to show fading compared to the unfiltered
magnitude of 17.0 reported by Lipunov et al. (GCN Circ. 23091).

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.

We thank Vladimir Lipunov for bringing this observation to our attention.