TITLE: GCN CIRCULAR NUMBER: 30807 SUBJECT: Swift GRB210910.42: Global MASTER-Net observations report DATE: 21/09/11 01:16:27 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-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB210910.42 (trigger No 1072706,15h 55m 05.47s , -54d 03m 16.6s, R=0.05) errorbox 50906 sec after notice time and 50940 sec after trigger time at 2021-09-11 00:20:55 UT, with upper limit up to 15.3 mag. The observations began at zenith distance = 41 deg. The sun altitude is -25.7 deg. The galactic latitude b = -1 deg., longitude l = 328 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1716320 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 51030 | MASTER-OAFA | C | 180 | 15.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.