TITLE:   GCN CIRCULAR
NUMBER:  26891
SUBJECT: GRB 200125A: Further RATIR Optical Observations and Confirmation of Fading
DATE:    20/01/26 21:08:51 GMT
FROM:    Alan M Watson at UNAM  <alan@astro.unam.mx>

Alan M. Watson (UNAM), Nat Butler (ASU), Alexander Kutyrev (GSFC),
William H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J.
Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI),
Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz
(UCSC), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Harvey
Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (U. Wash.), and Vicki
Toy (UMD) report:

We observed the field of GRB 200125A (Lien et al., GCN Circ. 26876) with
the Reionization and Transients Infrared Camera (RATIR; www.ratir.org)
on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico
Nacional on Sierra San Pedro Mártir from 2020/01 26.42 to 2020/01 26.56
UTC (22.62 to 25.89 hours after the BAT trigger), obtaining a total of
2.52 hours exposure in the r and i bands.

The source we reported previously (Watson et al., GCN Circ. 26882) has
faded, confirming that it is the afterglow. In comparison with the
USNO-B1 and 2MASS catalogs, we obtain the following detections:

  r	= 23.03 +/- 0.29
  i	= 21.27 +/- 0.05

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.

We thank the staff of the Observatorio Astronómico Nacional in San Pedro 
Mártir.