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GCN Circular 40769

Subject
Swift GRB 250617B: Global MASTER-Net observations report
Date
2025-06-18T06:36:55Z (3 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, 
G.Antipov,  A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez  (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) 

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 Swift GRB 250617B ( K. L. Page et al., GCN 40760Loading...
 
 ) errorbox  30652 sec after notice time and 30775 sec after trigger time at 2025-06-18 05:34:46 UT, with upper limit up to  18.6 mag. The observations began at zenith distance = 80 deg. The sun  altitude  is -74.8 deg. 

The galactic latitude b = -19 deg., longitude l = 89 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2906362

We obtain a following upper limits.  

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

   30866 |         MASTER-OAFA |   C |   180 | 17.3 |        
   31415 |         MASTER-OAFA |   C |    60 | 17.4 |        
   31495 |         MASTER-OAFA |   C |    60 | 17.7 |        
   32132 |         MASTER-OAFA |   C |   180 | 18.2 |        
   32767 |         MASTER-OAFA |   C |    60 | 18.1 |        
   32845 |         MASTER-OAFA |   C |    60 | 18.1 |        
   33417 |         MASTER-OAFA |   C |   180 | 18.6 |        
Filter C is a clear (unfiltred) band. 


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