GCN Circular 43148

Subject
Fermi trigger No 787736968: Global MASTER-Net observations report
Date
2025-12-18T12:30:39Z (11 hours 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  [1]  located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB251218.33 (trigger No 787736968,01h 20m 19.20s , +08d 31m 12.0s, R=2) errorbox  12771 sec after notice time and 12805 sec after trigger time at 2025-12-18 11:22:48 UT, with upper limit up to  15.0 mag. The observations began at zenith distance = 44 deg. The sun  altitude  is -21.0 deg. 

The galactic latitude b = -53 deg., longitude l = 136 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3075501

We obtain a following upper limits.  

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

   12835 | 2025-12-18 11:22:48 |        MASTER-Tunka | (01h 32m 31.99s , +10d 56m 59.4s) |   C |    60 | 15.0 |        
   12835 | 2025-12-18 11:22:48 |        MASTER-Tunka | (01h 32m 06.93s , +11d 03m 54.2s) |   C |    60 | 14.7 |        
   13495 | 2025-12-18 11:33:47 |        MASTER-Tunka | (01h 16m 38.29s , +09d 03m 21.8s) |   C |    60 | 14.6 |        
   13495 | 2025-12-18 11:33:47 |        MASTER-Tunka | (01h 16m 13.08s , +09d 10m 03.4s) |   C |    60 | 14.5 |        
   15014 | 2025-12-18 11:59:06 |        MASTER-Tunka | (01h 31m 58.57s , +09d 01m 47.3s) |   C |    60 | 13.3 |        
   15014 | 2025-12-18 11:59:06 |        MASTER-Tunka | (01h 31m 32.75s , +09d 08m 12.9s) |   C |    60 | 13.5 |        
Filter C is a clear (unfiltred) band. 


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

[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html