TITLE:   GCN CIRCULAR
NUMBER:  31003
SUBJECT: GRB 211023B: Mondy optical afterglow confirmation
DATE:    21/10/26 11:09:14 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the field of GRB 211023B (Dichiara  et al., GCN  30960) with 
AZT-33IK telescope of Sayan observatory (Mondy)  starting on 2021-10-23 
(UT) 21:23:21.  We obtained 60 images in R-filter. We confirm afterglow 
of the GRB 211023B (Dichiara  et al., GCN  30960; Kuin et al. GCN 30975; 
Kann et al. GCN 30995; O'Connor et al., GCN 31000; Rastinejad et al., 
GCN 31002).   Preliminary photometry of the afterglow in stacked images 
is following

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

2021-10-23 21:23:21  0.15613    R     15*60   20.46  0.31  20.5
2021-10-23 21:23:21  0.03297    R     60*60   20.97  0.40  20.9

The photometry is based on the nearby USNO-B1.0 stars
RA DEC R2
11:21:12.41280 +39:08:38.1120 15.33
11:21:05.20872 +39:04:33.9600 14.18

We note the obtained magnitudes are in agreement with  non-detections of 
the optical counterpart (Lipunov et al., GCN 30964; Pozanenko et al., 
GCN 30972; Watson et al., GCN 30973; Yu et al., GCN 30976).