TITLE:   GCN CIRCULAR
NUMBER:  30861
SUBJECT: GRB 210912A: LBT optical observations
DATE:    21/09/22 11:41:40 GMT
FROM:    Andrea Melandri at INAF-OAB  <andrea.melandri@inaf.it>

A. Rossi (INAF-OAS Bologna) report on behalf of the CIBO collaboration:

We observed the field of GRB 210912A (Troja et al., GCN 30820) in the r' band with the LBC imager mounted on LBT (Mt Graham, AZ, USA). We obtained 10min of imaging at the midtime 11:20 UT on 2021-09-17 (~5 days after the burst trigger).

We clearly detect the optical afterglow (Hu et al., GCN 30823; Pankov et al., GCN 30825; Kuin & Troja, GCN 30832; Kann et al. GCN 30834; Nicuesa Guelbenzu et al. GCN 30837) with the following preliminary AB magnitude:

r = 22.73 +- 0.05

calibrated against Pan-STARRS field stars. It is likely that this flux is significantly affected by host galaxy contamination (Kann et al. GCN 30829).

We acknowledge the excellent support from the LBTO and LBT-INAF staff, particularly A. Cardwell, J. Williams and D. Paris, in obtaining these observations.