GCN Circular 42011

Subject
Fermi trigger No 780609036: Global MASTER-Net observations report
Date
2025-09-26T20:30:38Z (6 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-SAAO robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB250926.83 (trigger No 780609036,19h 26m 38.40s , -80d 55m 48.0s, R=7.6) errorbox  112 sec after notice time and 144 sec after trigger time at 2025-09-26 19:52:55 UT, with upper limit up to  18.2 mag. The observations began at zenith distance = 54 deg. The sun  altitude  is -40.0 deg. 

The galactic latitude b = -29 deg., longitude l = 313 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3000539

We obtain a following upper limits.  

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

     160 | 2025-09-26 19:52:55 |         MASTER-SAAO | (00h 31m 12.67s , -84d 57m 34.6s) |   C |    30 | 16.7 |        
     205 | 2025-09-26 19:52:55 |         MASTER-SAAO | (00h 31m 12.74s , -84d 57m 34.5s) |   C |   120 | 17.8 |  Coadd 
     160 | 2025-09-26 19:52:55 |         MASTER-SAAO | (00h 52m 18.08s , -85d 11m 39.8s) |   C |    30 | 17.1 |        
     205 | 2025-09-26 19:52:55 |         MASTER-SAAO | (00h 52m 18.11s , -85d 11m 39.9s) |   C |   120 | 18.2 |  Coadd 
     214 | 2025-09-26 19:53:44 |         MASTER-SAAO | (00h 31m 11.30s , -84d 57m 37.0s) |   C |    40 | 17.0 |        
     214 | 2025-09-26 19:53:44 |         MASTER-SAAO | (00h 52m 17.26s , -85d 11m 41.8s) |   C |    40 | 17.4 |        
     278 | 2025-09-26 19:54:43 |         MASTER-SAAO | (00h 31m 10.47s , -84d 57m 38.0s) |   C |    50 | 17.4 |        
     278 | 2025-09-26 19:54:43 |         MASTER-SAAO | (00h 52m 16.41s , -85d 11m 42.8s) |   C |    50 | 17.8 |        
     352 | 2025-09-26 19:55:52 |         MASTER-SAAO | (00h 31m 09.08s , -84d 57m 36.9s) |   C |    60 | 17.1 |        
     352 | 2025-09-26 19:55:53 |         MASTER-SAAO | (00h 52m 14.97s , -85d 11m 43.7s) |   C |    60 | 17.6 |        
    1541 | 2025-09-26 20:15:41 |         MASTER-SAAO | (19h 47m 45.38s , -84d 30m 55.3s) |   C |    60 | 14.1 |        
    1541 | 2025-09-26 20:15:41 |         MASTER-SAAO | (19h 29m 45.92s , -84d 14m 40.6s) |   C |    60 | 15.1 |        
    1796 | 2025-09-26 20:19:57 |         MASTER-SAAO | (16h 56m 37.37s , -84d 03m 27.9s) |   C |    60 | 17.4 |        
Filter C is a clear (unfiltred) band. 


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