TITLE:   GCN CIRCULAR
NUMBER:  23864
SUBJECT: GRB 190203A: COATLI Optical Observations 
DATE:    19/02/04 14:21:01 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), Diego
González (UNAM), William H. Lee (UNAM), Margarita Pereyra (UNAM), Carlos
Román-Zúñiga (UNAM), Alexander Kutyrev (GSFC), and Eleonora Troja (GSFC)
report:

We observed the field of GRB 190203A (Lien et al., GCN Circ. 23845) 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 2019-02-04 02:39 to 2019-02-04
09:19 (from 10.9 to 17.6 hours after the trigger), obtaining a total of
3.2 hours of exposure in the w filter.

At the position of the UVOT afterglow candidate (Lien et al., GCN Circ.
23852), we do not detect anything to a 5-sigma limit of w = 22.4.

Our non-detection is consistent with the rapid fading seen by Lien et
al. (GCN Circ. 23845), Novichonok et al. (GCN Circ. 23846), Moskvitin et
al. (GCN Circ. 23847), and Lipunov (GCN Circ. 23850).

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 and the staff of the Observatorio
Astronómico Nacional.