TITLE:   GCN CIRCULAR
NUMBER:  32880
SUBJECT: GRB 221027B: COATLI Upper Limits
DATE:    22/10/28 18:36:57 GMT
FROM:    Rosa Leticia Becerra Godinez at Inst. de Astronoma,UNAM  <rbecerra@astro.unam.mx>

Rosa L. Becerra (UNAM), Alan M. Watson (UNAM), Nat Butler (ASU), Simone
Dichiara (PSU), Tzveti Dimitrova (ASU), Oc��lotl L��pez (UNAM), Diego
Gonz��lez (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Margarita
Pereyra (UNAM), Eleonora Troja (UTV/ASU) and report:

We observed the field of the GRB 221027B (Lien et al., GCN Circ. 32867)
with the COATLI 50-cm telescope and HUITZI f/8 imager at the Observatorio
Astron��mico Nacional on the Sierra de San Pedro M��rtir (
http://coatli.astroscu.unam.mx) from 2022-10-28 01:47 UTC to 02:13 UTC (6.6
hours after the trigger), obtaining a total of 750 seconds of exposure in
the r filter.

We do not detect any uncataloged sources within the XRT error region
(Beardmore et al., GCN Circ. 32868) to a 3-sigma limit of r > 21.4 mag.

Our photometry is calibrated against the Pan-STARRS1 catalog, is on an
approximate AB system, and is not corrected for Galactic extinction in the
direction of the GRB.

We thank the COATLI/HUITZI technical team and the staff of the Observatorio
Astron��mico Nacional.