TITLE:   GCN CIRCULAR
NUMBER:  40527
SUBJECT: Fermi GRB 250521D: Global MASTER-Net observations report
DATE:    25/05/22 19:15:49 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 250521D ( Fermi GBM team, GCN 40516) errorbox  74439 sec after notice time and 74480 sec after trigger time at 2025-05-22 19:03:16 UT, with upper limit up to  18.2 mag. The observations began at zenith distance = 63 deg. The sun  altitude  is -20.4 deg. 

The galactic latitude b = 10 deg., longitude l = 52 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2877804

We obtain a following upper limits.  

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

   74510 | 2025-05-22 19:03:16 |   MASTER-Kislovodsk | (18h 46m 09.15s , +22d 14m 31.3s) |   C |    60 | 17.9 |        
   74594 | 2025-05-22 19:04:40 |   MASTER-Kislovodsk | (18h 54m 44.61s , +22d 15m 50.5s) |   C |    60 | 17.4 |        
   74879 | 2025-05-22 19:09:25 |   MASTER-Kislovodsk | (18h 31m 37.29s , +20d 22m 21.4s) |   C |    60 | 18.2 |        
Filter C is a clear (unfiltred) band. 


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