GCN Circular 45677

Subject
Swift GRB 260921A: Global MASTER-Net observations report
Event
GRB 260921A
Date
2026-09-21T09:59:36Z (21 hours ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
M. Segura,  F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)

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 (Lomonosov MSU)

D.Buckley (SAAO),

A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
A.Sosnovskij (Lomonosov MSU)

A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)

R.Rebolo (The Instituto de Astrofisica de Canarias)

O.Gress, N.Budnev(ISU)


MASTER-OAFA robotic telescope  [1]  located in Argentina (OAFA observatory of San Juan National University) was pointed to the Swift GRB 260921A ( K. L. Page et al., GCN 45676Loading...
 
 ) errorbox  58 sec after notice time and 80 sec after trigger time at 2026-09-21 09:30:32 UT, with upper limit up to  15.5 mag. Observations started at twilight.  The observations began at zenith distance = 76 deg. The sun  altitude  is -12.8 deg. 

The galactic latitude b = 39 deg., longitude l = 233 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3508447

We obtain a following upper limits.  

Tmid-T0  |          Site       |Filt.| Expt. | Limit| Comment
_________|_____________________|_____|_______|______|________

      91 |         MASTER-OAFA |   C |    20 | 15.2 |        
     117 |         MASTER-OAFA |   C |    20 | 15.3 |        
     148 |         MASTER-OAFA |   C |    30 | 15.3 |        
     183 |         MASTER-OAFA |   C |    30 | 15.2 |        
     224 |         MASTER-OAFA |   C |    40 | 15.5 |        
     275 |         MASTER-OAFA |   C |    50 | 15.1 |        
     337 |         MASTER-OAFA |   C |    60 | 15.3 |        
     407 |         MASTER-OAFA |   C |    70 | 14.9 |        
     494 |         MASTER-OAFA |   C |    90 | 14.6 |        
     600 |         MASTER-OAFA |   C |   110 | 15.3 |        
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