GCN Circular 41849

Subject
Fermi GRB 250917B: Global MASTER-Net observations report
Event
GRB 250917B
Date
2025-09-17T12:31:52Z (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-Tunka robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 250917B ( Fermi GBM team, GCN 41846Loading...
 
 ) errorbox  21352 sec after notice time and 21386 sec after trigger time at 2025-09-17 12:24:10 UT, with upper limit up to  13.2 mag. Observations started at twilight.  The observations began at zenith distance = 22 deg. The sun  altitude  is -11.2 deg. 

The galactic latitude b = 19 deg., longitude l = 57 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2993668

We obtain a following upper limits.  

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

   21416 | 2025-09-17 12:24:10 |        MASTER-Tunka | (18h 22m 39.27s , +29d 57m 54.1s) |   C |    60 | 13.2 |        
   21498 | 2025-09-17 12:25:32 |        MASTER-Tunka | (18h 19m 56.75s , +28d 02m 47.7s) |   C |    60 | 13.0 |        
Filter C is a clear (unfiltred) band. 


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