TITLE:   GCN CIRCULAR
NUMBER:  40544
SUBJECT: Fermi GRB 250523A: Global MASTER-Net observations report
DATE:    25/05/23 20:31:57 GMT
FROM:    Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>

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-Kislovodsk robotic telescope  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) started inspect of the Fermi GRB 250523A ( Fermi GBM team, GCN 40538) errorbox  21017 sec after notice time and 21056 sec after trigger time at 2025-05-23 20:17:20 UT, with upper limit up to  17.1 mag. The observations began at zenith distance = 81 deg. The sun  altitude  is -25.3 deg. 

The galactic latitude b = -0 deg., longitude l = 145 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2879253

We obtain a following upper limits.  

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

   21087 | 2025-05-23 20:17:20 |   MASTER-Kislovodsk | (03h 30m 46.09s , +56d 01m 35.6s) |   C |    60 | 17.1 |        
   21175 | 2025-05-23 20:18:48 |   MASTER-Kislovodsk | (03h 45m 14.18s , +56d 02m 05.0s) |   C |    60 | 17.0 |        
   21462 | 2025-05-23 20:23:35 |   MASTER-Kislovodsk | (03h 02m 54.34s , +56d 12m 15.7s) |   C |    60 | 17.1 |        
   21545 | 2025-05-23 20:24:58 |   MASTER-Kislovodsk | (03h 17m 09.58s , +56d 11m 13.2s) |   C |    60 | 17.1 |        
Filter C is a clear (unfiltred) band. 


The observation and reduction will continue. 
The message may be cited.