TITLE:   GCN CIRCULAR
NUMBER:  34519
SUBJECT: GRB 230812B: Assy  optical observations, possible SN rise
DATE:    23/08/22 11:49:56 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>

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

We observed the field of GRB 230812B (Fermi GBM Team, GCN 34386;
Scotton et al., GCN 34392; Page et al. GCN 34394; Kuin et al.,
GCN 34399; Casentini et al., GCN 34402) with AZT-20 telescope of Assy-Turgen observatory  on 2023-08-17 -- 2023-08-21.

The OT (Lesage et al., GCN 34387; Scotton et al., GCN 34392; Page,
GCN 34394; Zheng & Filippenko, GCN 34395; Lipunov et al., GCN 34396;
Salgundi et al., GCN 34397; Ackley et al., GCN 34398; Xiong et al.,
GCN 34401; Casentini et al., GCN 34402; Frederiks et al., GCN 34403;
Mao et al., GCN 34404; Odeh et al., GCN 34405; Moskvitin & Spiridonova,
GCN 34406; Leonini et al., GCN 34408; de Ugarte Postigo et al.,
GCNs 24409, 34410; Belkin et al. GCN 34412; Ruocco et al. GCN 34413;
Frederiks et al. GCN 34414; Ruocco et al. GCN 34415; Shrestha et al.
GCN 34416; Quadri et al. GCN 34417; Adami et al. GCN 34418;
Moretti et al. GCN 34419; Kumar et al. GCN 34420; Belkin et al. GCNs
34421, GCN 34423; Pyshna et al., GCN 34425; Moskvitin & Spiridonova,
GCN 34428; Quadri & Strabla, GCN 34430; Mihov et al., GCN 34431;
Belkin et al. GCN 34432; Klose et al., GCN 34435; Scarfi, GCN 34436;
Moskvitin & Spiridonova, GCNs 34442, 34461, 34471, 34475;
Vinko et al., GCN 34463; H. Kumar et al., GCN 34500; Turpin et al.,
GCN 34508) is clearly detected.

Preliminary photometry of the OT is following

Telescope Date UTstart Exptime Filter t-T0 OT Err UL
                       sec            days
AZT-20 2023-08-17 16:51:34 60x60 r 4.932892 21.70 0.05 23.9
AZT-20 2023-08-17 18:14:50 60x60 i 4.990722 21.87 0.10 23.2
AZT-20 2023-08-18 16:47:02 60x60 r 5.929748 21.71 0.07 23.8
AZT-20 2023-08-18 18:05:43 60x60 i 5.984388 21.73 0.10 23.2
AZT-20 2023-08-20 16:15:33 60x60 r 7.907882 21.70 0.04 24.1
AZT-20 2023-08-20 17:37:12 60x60 i 7.964583 21.82 0.09 23.3
AZT-20 2023-08-21 16:31:06 60x60 r 8.918678 21.61 0.05 23.3
AZT-20 2023-08-21 17:51:59 80x60 i 8.981796 21.39 0.06 23.4

The photometry is based on nearby SDSS stars.
SDSS-DR12
RA Dec r i
16:36:25.6 +47:53:20.5 17.018 16.857
16:36:25.2 +47:52:20.9 16.229 16.106

After plateau phase between Aug. 15 - Aug.20  at r ~ 21.7, i~ 21.8 which is brighter than a host galaxy (e.g. Legacy Survey DR10 Catalog the host is r~22.66 (Belkin et al., GCN 34412)) the OT is brightening and we can confirm  the OT  brightening (Moskvitin et al., GCN 34516) which   could be related with a supernova rise. The supernova rise have beed also suggested by GIT (GCN 34500).