GRB 210227.19

V. Lipunov, E. Gorbovskoy, V.Kornilov, D.Kuvshinov, N.Tyurina, P.Balanutsa,
A.Kuznetsov, A.V. Krylov, I. Gorbunov, D. Vlasenko, F. Balakin
Lomonosov Moscow State University,
Sternberg Astronomical Institute, Moscow State University

R. Podesta, Carlos Lopez and F. Podesta
Observatorio Astronomico Felix Aguilar (OAFA)

A. Tlatov, V.Senik, A.V. Parhomenko, D. Dormidontov
Kislovodsk Solar Station of the Pulkovo Observatory

V. Yurkov, A. Gabovich, Yu. Sergienko
Blagoveschensk Educational State University, Blagoveschensk

K. Ivanov, O. Gres, N.M. Budnev, S.Yazev, O. Chuvalaev, V. Poleshchuk
Irkutsk State University

D. Buckley, S. Potter, A. Kniazev, M. Kotze
South African Astronomical Observatory

R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres
The Instituto de Astrofisica de Canarias

MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the  GRB210227.19 42 sec after notice time and 52 sec after trigger time at 2021-02-27 04:34:46 UT. On our 4-th (30s exposure)  set , obtained 157 sec after tigger time at 2021-02-27 04:36:30 UT, we  found 1 optical transient within Integral error-box (ra=84.7625 dec=17.8122 r=0.05) brighter than  14.5.


 T-Tmid      Date      Time       Expt.        Ra                Dec           Mag
---------|---------------------|-------|-----------------|-----------------|-------
     172   2021-02-27 04:36:30      30   (05h 39m 11.68s , +17d 49m 09.6s)     13.1

The 5-sigma upper limit has been about  14.5mag
The message may be cited.

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-OAFA robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Argentina (OAFA observatory of San Juan National University) was pointed to the Integral GRB210227.19 (trigger No 9020,05h 39m 03.41s , +17d 48m 45.2s, R=0.0488333) errorbox  41 sec after notice time and 52 sec after trigger time at 2021-02-27 04:34:46 UT, with upper limit up to  15.0 mag. The observations began at zenith distance = 85 deg. The sun  altitude  is -50.5 deg. 

The galactic latitude b = -6 deg., longitude l = 189 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=1556892

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      58 |         MASTER-OAFA |   C |    10 | 14.7 |        
      91 |         MASTER-OAFA |   C |    10 | 14.6 |        
     128 |         MASTER-OAFA |   C |    20 | 14.8 |        
     172 |         MASTER-OAFA |   C |    30 | 15.0 |        
     226 |         MASTER-OAFA |   C |    40 | 15.0 |        
     371 |         MASTER-OAFA |   C |    70 | 14.6 |        
Filter C is a clear (unfiltred) band. 


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

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),
R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico FelixAguilar OAFA),
R. Rebolo, M. Serra(The Instituto de Astrofisica de Canarias),
D. Buckley (South African Astronomical Observatory),
O.A. Gres, N.M. Budnev (Irkutsk State University, API),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)

MASTER collaboration reports:
MASTER OT, publishied in GCN 29580
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 , is not new optical source, but is 
known bright star (error in coordinates detection was from bad weather conditions)

We apologize for any confusion this error may have caused.