TITLE:   GCN CIRCULAR
NUMBER:  23481
SUBJECT: GRB 181201A: COATLI Optical Detection
DATE:    18/12/02 06:37:42 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan@astro.unam.mx>

Alan M. Watson (UNAM), Margarita Pereyra (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 GRB 181201A (Mereghetti et al., GCN 23469) 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 2018-12-02 01:39:01 to 04:02:58
(from 23.0 to 25.4 hours after the trigger), obtaining a total of 1.89
hours of exposure in the w filter.

We detect the optical counterpart reported by Podesta et al. (GCN Circ.
23470) at w = 17.82 +/- 0.01.

Our w magnitudes are calibrated against the USNO-B1 catalog (adjusted to
an approximate AB system) and are 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.