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GCN Circular 23092

Subject
GRB 180806.94: COATLI Detection of MASTER OT J004613.05+242014.1 and Confirmation of Fading
Date
2018-08-07T12:11:36Z (6 years ago)
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 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 Astron��mico Nacional on the Sierra de San Pedro M��rtir
(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 ��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.

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