TITLE:   GCN CIRCULAR
NUMBER:  24287
SUBJECT: GRB 190427A: COATLI Optical Observations 
DATE:    19/04/27 15:13:14 GMT
FROM:    Alan M Watson at UNAM  <alan@astro.unam.mx>

Alan M. Watson (UNAM), Eleonora Troja (GSFC), Nat Butler (ASU), Rosa L.
Becerra (UNAM), Diego González (UNAM), William H. Lee (UNAM), Margarita
Pereyra (UNAM), Carlos Román-Zúñiga (UNAM) and Alexander Kutyrev (GSFC)
report:

We observed the field of GRB 190427A (Tohuvavohu et al., GCN Circ.
24261) 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 05:28:30 to 06:36:27
(from 0.9 to 2.0 hours after the trigger), obtaining a total of 3000
seconds of exposure in the w filter.

Comparing to the USNO and Pan-STARRS1 catalogs, we do not detect any new
sources brighter than w = 21 in the BAT error region.

Our w magnitudes are calibrated against the Pan-STARRS1 catalog, are on 
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.