TITLE: GCN CIRCULAR NUMBER: 30766 SUBJECT: Swift GRB 210905A: Global MASTER-Net observations report DATE: 21/09/05 00:32:44 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-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) was pointed to the Swift GRB 210905A ( E. Sonbas et al., GCN 30765) errorbox 6 sec after notice time and 414 sec after trigger time at 2021-09-05 00:19:36 UT, with upper limit up to 19.1 mag. The observations began at zenith distance = 48 deg. The sun altitude is -55.5 deg. The galactic latitude b = -37 deg., longitude l = 356 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1709881 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 455 | MASTER-SAAO | P\ | 80 | 18.2 | 565 | MASTER-SAAO | P\ | 300 | 19.1 | Coadd 556 | MASTER-SAAO | P\ | 100 | 18.3 | 678 | MASTER-SAAO | P\ | 120 | 18.5 | 826 | MASTER-SAAO | P\ | 150 | 18.5 | The observation and reduction will continue. The message may be cited.