GCN Circular 44180

Subject
Fermi GRB 260401A: Global MASTER-Net observations report
Event
GRB 260401A
Date
2026-04-02T06:00:50Z (3 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 260401A ( Fermi GBM team, GCN 44174Loading...
 
 ) errorbox  63483 sec after notice time and 63518 sec after trigger time at 2026-04-02 04:32:04 UT, with upper limit up to  19.0 mag. The observations began at zenith distance = 29 deg. The sun  altitude  is -63.7 deg. 

The galactic latitude b = 38 deg., longitude l = 337 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3225119

We obtain a following upper limits.  

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

   33732 | 2026-04-01 20:15:08 |             MASTER- | (14h 42m 26.86s , -15d 41m 21.2s) |   C |    60 | 12.9 |        
   63549 | 2026-04-02 04:32:04 |         MASTER-OAFA | (14h 25m 14.66s , -15d 38m 17.7s) |   C |    60 | 18.4 |        
   63609 | 2026-04-02 04:32:04 |         MASTER-OAFA | (14h 25m 14.66s , -15d 38m 17.8s) |   C |   180 | 19.0 |  Coadd 
   63624 | 2026-04-02 04:33:19 |         MASTER-OAFA | (14h 25m 11.96s , -15d 36m 34.5s) |   C |    60 | 18.3 |        
   63700 | 2026-04-02 04:34:36 |         MASTER-OAFA | (14h 25m 12.06s , -15d 37m 47.2s) |   C |    60 | 18.4 |        
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