GCN Circular 43150

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-Kislovodsk robotic telescope  [1]  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the IceCube Alert 251218.85 (trigger No 9008919,23h 34m 08.64s , +44d 08m 42.0s, R=0.51) errorbox  64 sec after notice time and 107 sec after trigger time at 2025-12-18 20:22:48 UT, with upper limit up to  17.0 mag. The observations began at zenith distance = 57 deg. The sun  altitude  is -68.4 deg. 

MASTER-Tunka robotic telescope  located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the IceCube Alert 251218.85 errorbox  247 sec after notice time and 290 sec after trigger time at 2025-12-18 20:25:51 UT, with upper limit up to  18.0 mag. The observations began at zenith distance = 80 deg. The sun  altitude  is -42.5 deg. 

The galactic latitude b = -16 deg., longitude l = 109 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3076097

We obtain a following upper limits.  

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

     117 | 2025-12-18 20:22:48 |   MASTER-Kislovodsk | (23h 32m 34.10s , +44d 07m 24.4s) |  P- |    20 | 16.8 |        
     117 | 2025-12-18 20:22:48 |   MASTER-Kislovodsk | (23h 32m 25.71s , +44d 29m 51.7s) |  P| |    20 | 16.9 |        
     162 | 2025-12-18 20:23:28 |   MASTER-Kislovodsk | (23h 32m 33.96s , +44d 07m 21.9s) |  P- |    30 | 17.0 |        
     321 | 2025-12-18 20:25:51 |        MASTER-Tunka | (23h 34m 38.20s , +44d 21m 36.4s) |   C |    60 | 18.0 |        
     321 | 2025-12-18 20:25:51 |        MASTER-Tunka | (23h 34m 16.79s , +44d 26m 39.9s) |   C |    60 | 17.5 |        
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