[vsnet-grb-info 21762] GRB 190204A: COATLI Optical Detection of the Fading Afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23861
SUBJECT: GRB 190204A: COATLI Optical Detection of the Fading Afterglow 
DATE:    19/02/04 12:54:35 GMT
FROM:    Alan M. Watson at Instituto de Astronomia UNAM  <alan at 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 190204A (Lien et al., GCN Circ. 23852) 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 05:46:35 to 2019-02-04
05:57:30 (from 34 to 689 seconds after the trigger), obtaining a total
of 345 seconds of exposure in the w filter.

At the position of the UVOT afterglow candidate (Lien et al., GCN Circ.
23852), we detect a source that fades from w = 13.5 to w = 17.5 over the
course of our observations. A power-law fit suggest a temporal index of
-1.44 +/- 0.03.

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.