TITLE:   GCN CIRCULAR
NUMBER:  29635
SUBJECT: GRB 210306A: continued Mondy optical observations
DATE:    21/03/09 06:31:50 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Belkin (IKI),  A. Pozanenko (IKI), E. Klunko (ISTP), N. Pankov (HSE) 
report  on behalf of GRB IKI FuN:

We continue observations (Belkin et al., GCNs 29616,29620)  the field of 
GRB 210306A (D'Elia et al., GCN 29597; Ohno et al., GCN 29602) with 
AZT-33IK telescope of Sayan observatory (Mondy). The optical afterglow 
(D'Elia et al., GCN 29597; Watson et al., GCN 29598; Romanov, GCN 29599; 
Strausbaugh et al., GCN 29600; Hentunen et al., GCN 29603; Stecklum et 
al., GCN 29604; Lipunov et al. GCN 29606, Zhu et al. GCN 29607; Hosokawa 
et al., GCN  29608; Dimple et al., GCN 29618) is detected in a combined 
image. Preliminary photometry of the afterglow in the combined image is 
following

Date       UT start   t-T0       Filter Exp.    OT    Err.  UL(3sigma)
                       (mid, days)        (s)

2021-03-08 13:47:43   2.43317    R      30*120  22.68 0.18  22.9

The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
1501-0181731 15.23
1502-0183049 17.69
1501-0181697 17.11