TITLE: GCN CIRCULAR NUMBER: 34476 SUBJECT: Swift GRB230818.98: Global MASTER-Net OT detection DATE: 23/08/18 23:32:12 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, V.Kornilov, E.Gorbovskoy, K.Zhirkov, N.Tyurina, P.Balanutsa, A.Kuznetsov, D. Vlasenko, G.Antipov, D.Zimnukhov, V.Senik, E.Minkina, A.Chasovnikov, V.Topolev, D.Kuvshinov, D. Cheryasov, Ya.Kechin, Yu.Tselik (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O.A. Gress, N.M. Budnev (Irkutsk State University, API), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich (Blagoveschensk Educational State University) MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the GRB230818.98 22 sec after notice time and 37 sec after trigger time at 2023-08-18 23:28:11 UT. On our first (10s exposure) set we found 1 optical transient within Swift error-box (ra=285.879 dec=40.8758 r=0.05) brighter than 16.8. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 42 2023-08-18 23:28:11 10 (19h 03m 33.11s , +40d 53m 48.5s) 15.5 The 5-sigma upper limit has been about 16.8mag The message may be cited.