TITLE:   GCN CIRCULAR
NUMBER:  23781
SUBJECT: GRB 190123A: COATLI Optical Observations 
DATE:    19/01/24 12:51:10 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 190123A (D'Ai et al., GCN Circ. 23769) 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 2019-01-24 02:30 to 2019-01-23
10:56 (from 14.2 to 22.6 hours after the trigger), obtaining a total of
6.7 hours of exposure in the w filter.

We do not detect a source at the enhanced XRT position (Beardmore et
al., GCN Circ. 23771) to a 5-sigma upper limit of w > 22.9.

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.

Our deeper non-detection follows non-detections reported by Lipunov et
al. (GCN Circ. 23770), Hu et al. (GCN Circ. 23772), Steeghs et al. (GCN
Circ. 23774), and Shiraishi et al.(GCN Circ. 23778).

We thank the COATLI technical team and the staff of the Observatorio
Astronómico Nacional.