TITLE:   GCN CIRCULAR
NUMBER:  29645
SUBJECT: GRB 210306A: LBT observations
DATE:    21/03/11 12:21:33 GMT
FROM:    Andrea Rossi at INAF  <andrea.rossi@inaf.it>

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

We observed the field of GRB 210306A (D'Elia et al., GCN 29597) 
simultaneously in the r' and z' bands with the LBC imager mounted on LBT 
(Mt Graham, AZ, USA). We obtained 20min of imaging on 2021-03-11, 5.06 
days after the burst trigger. Observations were performed under good 
weather conditions with an average seeing of ~1.2".

We clearly detect the afterglow and we preliminary measure

r=24.2+-0.2 (AB system),

calibrated against SDSS field stars. This is still in agreement with the 
late decay index alpha~1.1 (after an initial plateau ending at ~2hours 
after the burst trigger) obtained modelling the photometry available 
(Strausbaugh et al., GCN29600; Zhu et al., GCN 29607; Hentunen & 
Nissinen GCN 29603; Hosokawa et al., GCN29608; Dimple et al., GCN 29618; 
Belkin et al., GCN 29616, GCN 29620, 29635; Klose et al., GCN 29644).

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