GCN Circular 44453

Subject
Fermi GRB 260504A: Global MASTER-Net observations report
Event
GRB 260504A
Date
2026-05-04T09:46:26Z (5 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-OAFA robotic telescope  [1]  located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260504A ( Fermi GBM team, GCN 44452Loading...
 
 ) errorbox  578 sec after notice time and 612 sec after trigger time at 2026-05-04 09:23:10 UT, with upper limit up to  16.5 mag. The observations began at zenith distance = 79 deg. The sun  altitude  is -22.5 deg. 

The galactic latitude b =  5 deg., longitude l = 86 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3291732

We obtain a following upper limits.  

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

     672 | 2026-05-04 09:23:10 |         MASTER-OAFA | (20h 30m 50.42s , +46d 55m 36.5s) |   C |   120 | 16.4 |        
     813 | 2026-05-04 09:25:16 |         MASTER-OAFA | (20h 30m 48.57s , +46d 55m 44.3s) |   C |   150 | 16.1 |        
     924 | 2026-05-04 09:27:52 |         MASTER-OAFA | (20h 30m 47.07s , +46d 55m 48.4s) |   C |    60 | 16.4 |        
     990 | 2026-05-04 09:28:58 |         MASTER-OAFA | (20h 30m 46.11s , +46d 55m 50.2s) |   C |    60 | 16.5 |        
    1056 | 2026-05-04 09:30:03 |         MASTER-OAFA | (20h 30m 45.24s , +46d 55m 54.1s) |   C |    60 | 16.4 |        
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