GCN Circular 43921

Subject
Fermi GRB 260305A: Global MASTER-Net observations report
Event
GRB 260305A
Date
2026-03-05T03:00:46Z (a month 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  [1]  located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260305A ( Fermi GBM team, GCN 43920Loading...
 
 ) errorbox  55 sec after notice time and 87 sec after trigger time at 2026-03-05 02:43:05 UT, with upper limit up to  18.6 mag. The observations began at zenith distance = 70 deg. The sun  altitude  is -22.7 deg. 

The galactic latitude b = 68 deg., longitude l = 57 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3169780

We obtain a following upper limits.  

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

      98 | 2026-03-05 02:43:05 |         MASTER-SAAO | (14h 27m 04.56s , +37d 55m 52.3s) |   C |    20 | 17.2 |        
      98 | 2026-03-05 02:43:05 |         MASTER-SAAO | (14h 24m 55.60s , +38d 11m 54.7s) |   C |    20 | 17.0 |        
     217 | 2026-03-05 02:44:55 |         MASTER-SAAO | (14h 12m 08.18s , +34d 56m 29.5s) |   C |    40 | 17.4 |        
     272 | 2026-03-05 02:44:55 |         MASTER-SAAO | (14h 12m 08.18s , +34d 56m 29.4s) |   C |   150 | 18.6 |        
     217 | 2026-03-05 02:44:55 |         MASTER-SAAO | (14h 14m 11.70s , +34d 40m 22.7s) |   C |    40 | 17.6 |        
     272 | 2026-03-05 02:44:55 |         MASTER-SAAO | (14h 14m 11.71s , +34d 40m 22.8s) |   C |   150 | 18.4 |        
     281 | 2026-03-05 02:45:54 |         MASTER-SAAO | (14h 14m 11.94s , +34d 40m 26.1s) |   C |    50 | 17.8 |        
     281 | 2026-03-05 02:45:54 |         MASTER-SAAO | (14h 12m 08.41s , +34d 56m 34.1s) |   C |    50 | 17.5 |        
     355 | 2026-03-05 02:47:03 |         MASTER-SAAO | (14h 12m 08.69s , +34d 56m 39.2s) |   C |    60 | 17.7 |        
     355 | 2026-03-05 02:47:03 |         MASTER-SAAO | (14h 14m 12.16s , +34d 40m 30.0s) |   C |    60 | 17.8 |        
     625 | 2026-03-05 02:51:33 |         MASTER-SAAO | (14h 24m 26.43s , +33d 57m 36.0s) |   C |    60 | 17.8 |        
     625 | 2026-03-05 02:51:33 |         MASTER-SAAO | (14h 22m 22.92s , +34d 13m 45.5s) |   C |    60 | 17.5 |        
     704 | 2026-03-05 02:52:52 |         MASTER-SAAO | (14h 24m 26.68s , +33d 57m 40.9s) |   C |    60 | 17.8 |        
     704 | 2026-03-05 02:52:52 |         MASTER-SAAO | (14h 22m 23.24s , +34d 13m 52.3s) |   C |    60 | 17.7 |        
     784 | 2026-03-05 02:54:11 |         MASTER-SAAO | (14h 22m 23.58s , +34d 13m 57.5s) |   C |    60 | 17.7 |        
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