TITLE:   GCN CIRCULAR
NUMBER:  29094
SUBJECT: GRB 201209A: Mondy optical observations, afterglow confirmation
DATE:    20/12/20 10:46:03 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the field of  GRB 201209A (Gropp et al., GCN 29005) with 
AZT-33IK telescope of Sayan observatory (Mondy) starting on Dec. 09 (UT) 
  11:41:13 (i.e. 0.28 days) and next epochs later. We detected a weak 
source within enhanced XRT position (Goad et al., GCN 29005) at ~1.4 
days after GRB 201209A trigger and not detected in other epochs.  Thus 
we confirm the optical afterglow detection on 0.321 days at R = 22.05 
+/- 0.16 (Zhu et al. GCN 29013).

Preliminary photometry of the field and afterglow is following

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

2020-12-09  11:41:13  42*120  R        0.27873   n/d    n/d  21.7
2020-12-10  14:26:13  45*120  R        1.39332   23.4   0.3  23.5
2020-12-12  11:14:21  39*120  R        3.25868   n/d    n/d  22.2
2020-12-13  12:03:41  38*120  R        4.26307   n/d    n/d  22.9

The photometry is based on nearby USNO-B1.0 stars.