TITLE:   GCN CIRCULAR
NUMBER:  32645
SUBJECT: GRB 221009A (Swift J1913.1+1946): Mondy optical observations
DATE:    22/10/10 08:10:47 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed GRB 221009A (Swift J1913.1+1946) (Swift-BAT detection of 
Swift J1913.1+1946: Dichiara et al., GCN 32632; Kennea and Williams, GCN 
  32635; Fermi-GBM detection: Veres et al., GCN  32636; Fermi-LAT 
detection: Bissaldi et al., GCN  32636, IPN localization: Svinkin et 
al., GCN 32641) with AZT-33IK telescope of Sayan observatory (Mondy) 
starting on 2022-10-09 (UT) 14:26:54 and continuing to 15:34:05.

We clearly detect the optical afterglow (Dichiara et al., GCN 32632; 
Lipunov et al., GCN 32634; Perley GCN 32638; Hu et al., GCN 32644). 
Preliminary photometry of the afterglow at the first image is following

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

2022-10-09 14:26:54  0.01223     R      120    14.84 0.09  20.8

We observe a monotonic decay in brightness, which can be approximated by 
a power law with an index of -0.52.

The photometry is based on the nearby USNO-B1.0 stars (R2)