TITLE:   GCN CIRCULAR
NUMBER:  29620
SUBJECT: GRB 210306A: continued Mondy optical observations
DATE:    21/03/08 11:16:12 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., GCN 29616)  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 still 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)

2021-03-07 13:43:24   1.41281    R      5*120  22.09 0.25  22.1

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 17.1