TITLE:   GCN CIRCULAR
NUMBER:  32818
SUBJECT: GRB 221009A: optical observations, SN photometric evidence
DATE:    22/10/22 22:47:16 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Belkin (IKI, HSE), A. Moskvitin (SAO RAS), V. Kim (FAI), A. Pozanenko 
(IKI),  M. Krugov (FAI), R. Uklein (SAO RAS), N. Pankov (HSE) report on 
behalf of GRB IKI FuN:

We continue observations of GRB 221009A (Swift J1913.1+1946) (Dichiara 
et al., GCN 32632; Kennea and Williams, GCN  32635; Veres et al., GCN 
32636; Bissaldi et al., GCN  32636; Svinkin et al., GCN 32641; Piano et 
al., GCN 32657; Pillera et al., GCN 32658;  Gotz et al., GCN 32660; Xiao 
et al., GCN 32661; Frederiks et al., GCN 32668; GCN 32668; Ripa
et al., GCN 32685; Kozyrev et al., GCN 32805).  Observations  with 
AZT-20 telescope of Assy-Turgen observatory obtained on  October 20, 21 
and TOO photometry with BTA SAO RAS telescope equipped with SCORPIO-2 
was obtained on  October 16 and 18.  The optical afterglow (GCNs 32632, 
  32635, 32636, 32641, 32657, 32658, 32660, 32666, 32668, 32670, 32671, 
32676, 32677, 32678, 32679, 32680, 32683, 32684, 32685, 32686, 32691, 
32692, 32693, 32694, 32695, 32700, 32705, 32707, 32709, 32727, 32729, 
32730, 32736, 32738, 32739, 32740, 32743, 32746, 32749, 32750; 32752; 
32753; 32755; 32758; 32765; 32769; 32771; 32795; 32799; 32803; 32804; 
32809; 32811) is detected in combined images of g',r',i' filters.

Preliminary photometry of the afterglow on 2022-10-20/21 obtained in 
Assy observatory with  AZT-20 telescope is following

Date       UT start  t-T0       Exp.   Filter  OT    Err.   UL(3sigma)
                     (mid, days)  (s)           (AB)
2022-10-20/21 n/d   11.55024    59*60  g'      23.7   0.2   24.5
2022-10-21 14:18:18 12.05299    30*60  r'      21.94  0.07  23.9
2022-10-21 14:49:37 12.08516    30*60  i'      20.72  0.11  23.3

The photometry is based on nearby PS1 stars.

The light curve based on our observations can be found in 
http://grb.rssi.ru/GRB221009A/GRB221009A_lc_cc_15_cut.png

We observe a bump in the light curve starting on 6th days since trigger. 
The light curve is clearly chromatic at the bump. We  can assume that 
the chromatic bump is a supernova over an afterglow of GRB 221009A 
(Belkin et al., GCN 32769).