TITLE:   GCN CIRCULAR
NUMBER:  29869
SUBJECT: Fermi  trigger No 640695289: Global MASTER-Net observations report 
DATE:    21/04/21 19:30:19 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-Tavrida robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB210421.45 (trigger No 640695289,18h 08m 19.20s , +57d 09m 00.0s, R=2.13) errorbox  63 sec after notice time and 29500 sec after trigger time at 2021-04-21 19:06:25 UT, with upper limit up to  19.2 mag. The observations began at zenith distance = 59 deg. The sun  altitude  is -23.8 deg. 

The galactic latitude b = 28 deg., longitude l = 86 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1598312

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

   29590 | 2021-04-21 19:06:25 |      MASTER-Tavrida | (18h 05m 57.66s , +57d 18m 06.1s) |   C |   180 | 18.5 |        
   29770 | 2021-04-21 19:06:25 |      MASTER-Tavrida | (18h 05m 57.68s , +57d 18m 05.9s) |   C |   540 | 19.2 |  Coadd 
   29790 | 2021-04-21 19:09:44 |      MASTER-Tavrida | (18h 06m 04.40s , +57d 18m 11.5s) |   C |   180 | 18.5 |        
   29989 | 2021-04-21 19:13:04 |      MASTER-Tavrida | (18h 06m 00.51s , +57d 19m 50.6s) |   C |   180 | 18.7 |        
   30189 | 2021-04-21 19:16:23 |      MASTER-Tavrida | (18h 06m 00.35s , +57d 18m 29.6s) |   C |   180 | 18.5 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.