TITLE:   GCN CIRCULAR
NUMBER:  29683
SUBJECT: GRB 210321A: MASTER optical observation
DATE:    21/03/21 20:49:00 GMT
FROM:    Vladimir Lipunov at Moscow State U/Krylov Obs  <lipunov@xray.sai.msu.ru>

V. Lipunov, V.Kornilov, E.Gorbovskoy,N.Tiurina,P.Balanutsa,F.Balakin, 
V.Vladimirov, A.Kuznetsov,K.Zhirkov,D. Vlasenko, I.Gorbunov, D.Zimnukhov, 
V.Senik, A.Chasovnikov,A.Pozdnyakov,V.Topolev, D.Cheryasov(Lomonosov Moscow State University, SAI, Physics Department),
D. Buckley (South African Astronomical Observatory),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA),
R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias),
O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API),
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 Swift GRB 210321A (BAT:Dichiara et al. GCN 29677,Ttrig=07:13:51; 
XRT:Perri et al. GCN 29678,Beardmore et al. GCN29681;
UVOT: Siegel GCN29679), 
optical observations at MASTER-Tavrida at 2021-03-21 16:55:20UT, ~9.7h after trigger time,
with mlim=20.8m.
Swift optical counterpart (87.8947 +70.1305) isn't visible yet.

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