TITLE: GCN CIRCULAR NUMBER: 30901 SUBJECT: Swift GRB 210930A: Global MASTER-Net observations report DATE: 21/09/30 16:36:24 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (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. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (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 Swift GRB 210930A ( V. D'Elia et al., GCN 30897) errorbox 48786 sec after notice time and 48953 sec after trigger time at 2021-09-30 16:22:45 UT, with upper limit up to 17.2 mag. Observations started at twilight. The observations began at zenith distance = 59 deg. The sun altitude is -11.0 deg. The galactic latitude b = 68 deg., longitude l = 114 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1737711 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 32055 | MASTER- | C | 1 | 14.1 | 32055 | MASTER- | C | 1 | 15.1 | 36978 | MASTER- | C | 180 | 20.0 | 49043 | MASTER-Tavrida | C | 180 | 17.2 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.