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 Román-Zúñiga (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
Astronómico Nacional on the Sierra de San Pedro Mártir
(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 Ángeles, Oscar Chapa,
Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosalía Langarica,
Fernando Quirós, and Carlos Tejada) and the staff of the Observatorio
Astronómico Nacional.