GCN Circular 43912

Subject
Fermi GRB 260303B: Global MASTER-Net observations report
Event
GRB 260303B
Date
2026-03-03T19:17:13Z (7 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-SAAO robotic telescope  [1]  located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260303B ( Fermi GBM team, GCN 43907Loading...
 
 ) errorbox  20103 sec after notice time and 20130 sec after trigger time at 2026-03-03 18:59:50 UT, with upper limit up to  16.5 mag. The observations began at zenith distance = 82 deg. The sun  altitude  is -22.8 deg. 

The galactic latitude b = -87 deg., longitude l = 48 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3166705

We obtain a following upper limits.  

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

   20160 | 2026-03-03 18:59:50 |         MASTER-SAAO | (00h 37m 01.21s , -26d 50m 03.0s) |   C |    60 | 16.2 |        
   20252 | 2026-03-03 19:01:22 |         MASTER-SAAO | (00h 37m 03.97s , -26d 48m 23.8s) |   C |    60 | 16.5 |        
   20344 | 2026-03-03 19:02:54 |         MASTER-SAAO | (00h 36m 56.33s , -26d 49m 08.6s) |   C |    60 | 16.4 |        
   20466 | 2026-03-03 19:04:26 |         MASTER-SAAO | (00h 36m 55.39s , -26d 48m 01.6s) |   C |   120 | 15.8 |        
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