TITLE: GCN CIRCULAR NUMBER: 29669 SUBJECT: Swift GRB210318.13: Global MASTER-Net observations report DATE: 21/03/18 22:06:18 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs 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 GRB210318.13 (trigger No 1037335,17h 36m 55.88s , -35d 49m 19.2s, R=0.01) errorbox 65903 sec after trigger time at 2021-03-18 21:26:56 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 83 deg. The sun altitude is -52.2 deg. The galactic latitude b = -3 deg., longitude l = 354 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1571373 We obtain a following upper limits. Tmid-T0 | Site |Filt.| Expt. | Limit| Comment _________|_____________________|_____|_______|______|________ 65934 | MASTER-SAAO | C | 60 | 14.1 | 66013 | MASTER-SAAO | C | 60 | 14.5 | 66093 | MASTER-SAAO | C | 60 | 14.9 | 67868 | MASTER-SAAO | C | 60 | 17.3 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.