TITLE: GCN CIRCULAR NUMBER: 29738 SUBJECT: GRB 210330A: MASTER optical observation DATE: 21/03/30 21:27:39 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, A.Chasovnikov, F.Balakin, V.Kornilov, E.Gorbovskoy,P.Balanutsa, V.Vladimirov, A.Kuznetsov,K.Zhirkov,D. Vlasenko, N.Tiurina, I.Gorbunov, D.Zimnukhov, V.Senik, V.Topolev, D.Cheryasov (Lomonosov Moscow State University, SAI, Physics Department), D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev (Irkutsk State University, API), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA), R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity) MASTER Global robotic net (MASTER-Net:http://observ.pereplet.ru Lipunov et al.,2010,Advances in Astronomy,2010,30L) started GECAM GRB 210330A (D.Y.Guo et al. GCN 29739, Ttrigger=12:45:46.600 UTC, R.A.Dec.: 164.3d,-55.6d, er.-b.=5.1d) optical observations at MASTER-SAAO (located in South African Astronomical Observatory) 17496 sec after trigger time at 2021-03-30 17:37:23 UT at sunset, with upper limit up to 18.7 mag. Observations started at zenith distance = 43 deg. The sun altitude was -13.6 deg. The galactic latitude b = 4 deg., longitude l = 288 deg. Real time updated cover map and OT,that can be discovered, will be available here: https://master.sai.msu.ru/site/master2/observ.php?id=1580304 There are the following upper limits of the first images Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 17587 | 2021-03-30 17:37:23 | MASTER-SAAO | (10h 57m 26.66s , -55d 35m 44.3s) | C | 180 | 18.7 | 17787 | 2021-03-30 17:40:43 | MASTER-SAAO | (10h 57m 26.36s , -55d 34m 44.9s) | C | 180 | 18.6 | 17986 | 2021-03-30 17:44:02 | MASTER-SAAO | (11h 05m 32.80s , -55d 35m 42.8s) | C | 180 | 18.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited.