TITLE:   GCN CIRCULAR
NUMBER:  23492
SUBJECT: GRB 181201A: Further COATLI Optical Monitoring
DATE:    18/12/03 07:12:44 GMT
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), Margarita Pereyra (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 2018-12-03 01:30:45 to 04:14:39
(from 46.9 to 49.6 hours after the trigger), obtaining a total of 1.5
hours of exposure in the w filter.

We continue to detect the optical counterpart reported by Podesta et al.
(GCN Circ. 23470) at w = 18.77 +/- 0.02.

The counterpart has faded by about 1 magnitude since our previous
observations (Watson et al., GCN 23481). Further observations are
planned.

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.