GCN Circular 22859

Alan M. Watson (UNAM), Nat Butler (ASU), Rosa L. Becerra (UNAM), William
H. Lee (UNAM), Carlos Rom��n-Z����iga (UNAM), Alexander Kutyrev (GSFC), and
Eleonora Troja (GSFC) report:

We observed the field of GRB 180626A (Evans et al., GCN 22850
Not found
 
 
) with the
COATLI 50-cm telescope and interim imager at the Observatorio
Astron��mico Nacional on the Sierra de San Pedro M��rtir
(http://coatli.astroscu.unam.mx) from 2018-06-20 08:21:50.6 to
11:18:41.7 UTC (from 33.7 seconds after the trigger or 17.9 seconds
after the alert to 2.95 hours after the trigger), obtaining a total of
7020 seconds of exposure in the w filter.

Within the enhanced XRT error region (Osborne et al., GCN Circ. 22852
Not found
 
 
),
we detect the afterglow previously reported by Evans et al. (GCN Circ.
22850
Not found
 
 
), Martone et al. (GCN Circ. 22854
Not found
 
 
), and Breeveld et al. (GCN Circ.
22857
Not found
 
 
) with

  w = 21.4 +/- 0.9

In our first set of 30 images each of 5 seconds of exposure, from
08:21:50.6 to 08:27:10.1 UTC, we do not detect the afterglow with a
10-sigma limiting magnitude of

  w > 19.2

These magnitudes are calibrated against the Pan-STARRS1 catalog and 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 (Fernando ��ngeles, Oscar Chapa,
Salvador Cuevas, Alejandro Farah, Jorge Fuentes, Rosal��a Langarica,
Fernando Quir��s, and Carlos Tejada) and the staff of the Observatorio
Astron��mico Nacional.