TITLE:   GCN CIRCULAR
NUMBER:  28725
SUBJECT: GRB 201020B: Mondy optical observations
DATE:    20/10/21 17:09:41 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the field of  GRB 201020B (Fermi GBM team, GCN 28702; 
Malacaria et al., GCN 28710; Arimoto et al., GCN 28716; Ursi et al., GCN 
28714; Ridnaia et al., GCN 28723) with AZT-33IK telescope of Sayan 
observatory (Mondy) starting on Oct. 21 (UT)  14:20:10. The optical 
transient (Lipunov  et al. GCN 28718; Xu  et al. GCN 28719) is well 
detected in our images in R-filter.

Preliminary photometry of the optical transient in a combined image is 
following

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

2020-10-21 14:20:10   0.88629    R      60*60   18.99 0.03   22.7


The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
1670-0037414 16.74
1670-0037586 16.16