TITLE: GCN CIRCULAR NUMBER: 30977 SUBJECT: GRB 211023A: MASTER OT J045237.07+851925.2 - optical counterpart discovery DATE: 21/10/24 20:36:12 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> K.Zhirkov, V. Lipunov, E.Gorbovskoy, P.Balanutsa, A.Kuznetsov, O.Gress, G.Antipov, D. Vlasenko, N.Tiurina, D.Zimnukhov, V.Senik,V.Topolev, A.Chasovnikov, E.Minkina, V.Grinshpun, D.Cheryasov (Lomonosov MSU,SAI,PhysicsDepartment), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev (Irkutsk State University, API), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER Global robotic net (MASTER-Net:http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L) started inspect of the FERMI GRB 211023A ( Fermi GBM team, GCN 30958,ttrigger=13:05:43, Fermi LAT GCN 30961) errorbox just after sunset at 2021-10-23 15:12:50 UT (Lipunov et al. GCN 30970). MASTER OT J045237.07+851925.2 discovery MASTER-Kislovodsk auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source - optical counterpart of this GRB at (RA, Dec) = 04h 52m 37.07s +85d 19m 25.2s at 2021-10-23.65385 UT. Fast changing OT unfiltered magnitude at one of first images is 15.6m (mlim=18.9). There is no minor planet in MPC and any sources in VIZIER at this place. We have reference image on 2017-01-28.75669 UT with unfiltered mlim=19.9m. Deep images and possibly host galaxy spectral observations are required.