TITLE:   GCN CIRCULAR
NUMBER:  29616
SUBJECT: GRB 210306A: Mondy optical observations
DATE:    21/03/07 20:21:30 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 observed the field of GRB 210306A (D'Elia et al., GCN 29597; Ohno et 
al., GCN 29602) with AZT-33IK telescope of Sayan observatory (Mondy) 
starting on 2021-03-06  (UT) 14:50:30. 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) is clearly detected in a combined image. Preliminary 
photometry of the object in a combined image is following

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

2021-03-06 14:50:30   0.47677    R      30*120  20.48 0.05  22.0

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