TITLE:   GCN CIRCULAR
NUMBER:  30825
SUBJECT: GRB 210912A: Mondy optical afterglow confirmation
DATE:    21/09/12 17:21:48 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

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

We observed the field of GRB 210912A (Troja et al., GCN 30820) with 
AZT-33IK telescope of Sayan observatory (Mondy)  starting on 
2021-09-12(UT) 12:57:48.  We obtained 30 images in R-filter. We confirm 
the fading object suggested by Hu et al. (GCN 30823) as the optic 
afterglow of GRB 210912A.   Preliminary photometry of the object in 
stacked images is following

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

2021-09-12 12:57:48  0.10112    R     29*120   21.33 0.14  22.5

The photometry is based on the nearby USNO-B1.0 stars
RA DEC R2
08:39:12.26208 +79:12:37.1304 15.88
08:39:10.94880 +79:16:33.8916 15.26