GCN Circular 29724

N.Tiurina, V. Lipunov, V.Kornilov, E.Gorbovskoy,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),
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)
automatically started Swift  GRB 210323A (Gropp et al. GCN 29699
Not found
 
 
, Ttrigger=22:02:18UT, 
https://gcn.gsfc.nasa.gov/other/210323A.gcn3
Not found
 
 
)
optical observations at MASTER-Tunka (in ~100km of Mondy , Pozanenko et al. GCN 29708
Not found
 
 
)
at 2021-03-23 22:03:12UT with 10s expositions by MASTER-600 twin robotic telescope
and by MASTER-VWFC (very wide field cameras)at sunrise.

The Sun altitude at MASTER-Tunka and Mondy was -9.6, see alert location 
and conditions of observation at 
http://observ.pereplet.ru/images/tunka2021-03-23-22-03-13.jpg (webcamera).

The distance to Sun of GRB coordinates was 49.6deg., that made 18.4m OT 
detection little likelihood for the telescopes at this location and at this time.

MASTER observed this alert's error-box also at
MASTER-Tavrida (2021-03-24 02:07:41 UT, with upper limit 18.2),
MASTER-IAC (2021-03-24 03:40:27 UT, Lipunov et al. 29702),
and MASTER-OAFA (started at 2021-03-24 09:40:18UT), 
see cover map, limits and altitudes at 
https://master.sai.msu.ru/site/master2/observ.php?id=1575256

Reduction and analyses will continue.
This message may be cited.