TITLE:   GCN CIRCULAR
NUMBER:  28768
SUBJECT: GRB 201020B: continued Mondy optical observations
DATE:    20/10/24 09:51:25 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 IKI GRB FuN:

We continued observations of the 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)  on Oct. 22, 23. The optical afterglow (Lipunov et 
al., GCN 28718; Xu et al., GCN 28719; Belkin et al., GCN 28725; Breeveld 
& Lien, GCN 28743; Vinko et al., GCN 28750; Kumar et al., GCN 28753) 
with redshift of z= 0.804 (Kann  et al., GCN 28765) is  detected in our 
stacked 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)

2020-10-22 17:35:31   2.02195    R      60*60   20.40 0.05   23.0
2020-10-23 14:33:52   2.89719    R      32*120  20.99 0.26   21.1


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