GCN Circular 43198

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) was pointed to the EP251221a ( EP Team et al., GCN 43178
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 ) errorbox  25137 sec after notice time and 48513 sec after trigger time at 2025-12-22 11:07:39 UT, with upper limit up to  14.1 mag. The observations began at zenith distance = 80 deg. The sun  altitude  is -18.4 deg. 

MASTER-Kislovodsk robotic telescope  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the EP251221a errorbox  77221 sec after notice time and 1 days 14196 sec after trigger time at 2025-12-23 01:35:42 UT, with upper limit up to  18.3 mag. The observations began at zenith distance = 48 deg. The sun  altitude  is -32.6 deg. 

The galactic latitude b = 12 deg., longitude l = 193 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3080482

We obtain a following upper limits.  

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

   48543 | 2025-12-22 11:07:39 |        MASTER-Tunka | (06h 57m 20.46s , +23d 03m 38.7s) |   C |    60 | 14.1 |        
   48543 | 2025-12-22 11:07:39 |        MASTER-Tunka | (06h 57m 34.89s , +22d 56m 36.5s) |   C |    60 | 13.3 |        
   52254 | 2025-12-22 12:08:30 |             MASTER- | (07h 00m 06.39s , +23d 40m 37.8s) |   C |   180 | 18.9 |        
   52254 | 2025-12-22 12:08:30 |             MASTER- | (07h 00m 04.96s , +24d 36m 38.8s) |   C |   180 | 18.4 |        
  100687 | 2025-12-23 01:35:42 |   MASTER-Kislovodsk | (06h 57m 08.12s , +23d 26m 58.0s) |   C |   180 | 18.2 |        
  100687 | 2025-12-23 01:35:42 |   MASTER-Kislovodsk | (06h 56m 59.41s , +23d 49m 39.5s) |   C |   180 | 18.3 |        
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