GCN Circular 41664

Subject
Fermi GRB 250902B: Global MASTER-Net observations report
Event
GRB 250902B
Date
2025-09-03T03:31:08Z (a month 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  (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L)  located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250902B ( Fermi GBM team, GCN 41660Loading...
 
 ) errorbox  18838 sec after notice time and 18874 sec after trigger time at 2025-09-03 00:00:08 UT, with upper limit up to  18.6 mag. The observations began at zenith distance = 77 deg. The sun  altitude  is -59.1 deg. 

The galactic latitude b = -20 deg., longitude l = 208 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=2983003

We obtain a following upper limits.  

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

   18905 | 2025-09-03 00:00:08 |         MASTER-SAAO | (05h 20m 30.13s , -04d 32m 16.8s) |   C |    60 | 17.4 |        
   18905 | 2025-09-03 00:00:08 |         MASTER-SAAO | (05h 22m 16.39s , -04d 47m 44.4s) |   C |    60 | 13.4 |        
   19743 | 2025-09-03 00:14:07 |         MASTER-SAAO | (05h 20m 31.93s , -04d 32m 23.9s) |   C |    60 | 17.7 |        
   19743 | 2025-09-03 00:14:07 |         MASTER-SAAO | (05h 22m 18.01s , -04d 47m 48.8s) |   C |    60 | 16.7 |        
   19962 | 2025-09-03 00:17:46 |         MASTER-SAAO | (05h 27m 44.14s , -04d 30m 25.1s) |   C |    60 | 17.8 |        
   19962 | 2025-09-03 00:17:46 |         MASTER-SAAO | (05h 29m 30.52s , -04d 45m 52.0s) |   C |    60 | 16.8 |        
   20055 | 2025-09-03 00:19:19 |         MASTER-SAAO | (05h 35m 39.60s , -04d 30m 43.8s) |   C |    60 | 18.0 |        
   20055 | 2025-09-03 00:19:19 |         MASTER-SAAO | (05h 37m 26.17s , -04d 46m 09.6s) |   C |    60 | 15.7 |        
   20368 | 2025-09-03 00:24:32 |         MASTER-SAAO | (05h 20m 25.60s , -04d 32m 23.1s) |   C |    60 | 17.8 |        
   20368 | 2025-09-03 00:24:32 |         MASTER-SAAO | (05h 22m 12.33s , -04d 47m 48.4s) |   C |    60 | 17.1 |        
   20590 | 2025-09-03 00:28:14 |         MASTER-SAAO | (05h 27m 42.05s , -04d 30m 33.7s) |   C |    60 | 17.8 |        
   20590 | 2025-09-03 00:28:14 |         MASTER-SAAO | (05h 29m 28.33s , -04d 45m 56.0s) |   C |    60 | 17.1 |        
   20814 | 2025-09-03 00:31:58 |         MASTER-SAAO | (05h 35m 47.86s , -04d 30m 20.8s) |   C |    60 | 17.9 |        
   20814 | 2025-09-03 00:31:58 |         MASTER-SAAO | (05h 37m 33.96s , -04d 45m 44.0s) |   C |    60 | 16.9 |        
   21125 | 2025-09-03 00:37:08 |         MASTER-SAAO | (05h 20m 30.36s , -04d 31m 31.8s) |   C |    60 | 17.8 |        
   21125 | 2025-09-03 00:37:08 |         MASTER-SAAO | (05h 22m 17.39s , -04d 46m 55.0s) |   C |    60 | 17.4 |        
   21217 | 2025-09-03 00:38:41 |         MASTER-SAAO | (05h 27m 38.90s , -04d 32m 11.0s) |   C |    60 | 17.8 |        
   21218 | 2025-09-03 00:38:41 |         MASTER-SAAO | (05h 29m 25.88s , -04d 47m 33.9s) |   C |    60 | 17.3 |        
   21436 | 2025-09-03 00:42:19 |         MASTER-SAAO | (05h 35m 42.83s , -04d 30m 02.1s) |   C |    60 | 18.1 |        
   21436 | 2025-09-03 00:42:19 |         MASTER-SAAO | (05h 37m 29.66s , -04d 45m 25.2s) |   C |    60 | 17.6 |        
   21623 | 2025-09-03 00:45:27 |         MASTER-SAAO | (05h 28m 42.64s , -06d 25m 09.3s) |   C |    60 | 17.8 |        
   21623 | 2025-09-03 00:45:27 |         MASTER-SAAO | (05h 30m 29.96s , -06d 40m 32.5s) |   C |    60 | 17.5 |        
   21717 | 2025-09-03 00:47:00 |         MASTER-SAAO | (05h 36m 44.94s , -06d 23m 48.0s) |   C |    60 | 18.3 |        
   21717 | 2025-09-03 00:47:00 |         MASTER-SAAO | (05h 38m 32.18s , -06d 39m 10.9s) |   C |    60 | 17.8 |        
   21811 | 2025-09-03 00:48:35 |         MASTER-SAAO | (05h 20m 28.96s , -04d 31m 31.0s) |   C |    60 | 17.8 |        
   21811 | 2025-09-03 00:48:35 |         MASTER-SAAO | (05h 22m 16.10s , -04d 46m 53.7s) |   C |    60 | 17.6 |        
   21905 | 2025-09-03 00:50:09 |         MASTER-SAAO | (05h 27m 37.83s , -04d 32m 12.9s) |   C |    60 | 17.8 |        
   21905 | 2025-09-03 00:50:09 |         MASTER-SAAO | (05h 29m 24.93s , -04d 47m 35.3s) |   C |    60 | 17.6 |        
   22202 | 2025-09-03 00:55:06 |         MASTER-SAAO | (05h 21m 31.95s , -06d 24m 31.1s) |   C |    60 | 17.9 |        
   22202 | 2025-09-03 00:55:06 |         MASTER-SAAO | (05h 23m 19.48s , -06d 39m 55.5s) |   C |    60 | 17.9 |        
   22295 | 2025-09-03 00:56:39 |         MASTER-SAAO | (05h 35m 39.88s , -04d 30m 50.9s) |   C |    60 | 18.2 |        
   22295 | 2025-09-03 00:56:39 |         MASTER-SAAO | (05h 37m 26.70s , -04d 46m 15.3s) |   C |    60 | 17.9 |        
   22481 | 2025-09-03 00:59:44 |         MASTER-SAAO | (05h 28m 48.06s , -06d 25m 09.7s) |   C |    60 | 18.0 |        
   22481 | 2025-09-03 00:59:44 |         MASTER-SAAO | (05h 30m 35.49s , -06d 40m 34.0s) |   C |    60 | 17.9 |        
   22579 | 2025-09-03 01:01:23 |         MASTER-SAAO | (05h 36m 44.70s , -06d 25m 51.1s) |   C |    60 | 18.6 |        
   22579 | 2025-09-03 01:01:23 |         MASTER-SAAO | (05h 38m 32.64s , -06d 41m 14.1s) |   C |    60 | 18.4 |        
   22672 | 2025-09-03 01:02:56 |         MASTER-SAAO | (05h 20m 30.08s , -04d 32m 05.7s) |   C |    60 | 18.0 |        
   22672 | 2025-09-03 01:02:56 |         MASTER-SAAO | (05h 22m 17.93s , -04d 47m 28.7s) |   C |    60 | 18.0 |        
   22765 | 2025-09-03 01:04:29 |         MASTER-SAAO | (05h 27m 40.12s , -04d 30m 40.7s) |   C |    60 | 18.0 |        
   22765 | 2025-09-03 01:04:29 |         MASTER-SAAO | (05h 29m 27.84s , -04d 46m 03.6s) |   C |    60 | 17.9 |        
   23049 | 2025-09-03 01:09:13 |         MASTER-SAAO | (05h 21m 26.00s , -06d 25m 32.3s) |   C |    60 | 18.0 |        
   23049 | 2025-09-03 01:09:13 |         MASTER-SAAO | (05h 23m 14.50s , -06d 40m 55.7s) |   C |    60 | 18.0 |        
   23143 | 2025-09-03 01:10:46 |         MASTER-SAAO | (05h 35m 38.42s , -04d 29m 57.8s) |   C |    60 | 18.2 |        
   23143 | 2025-09-03 01:10:46 |         MASTER-SAAO | (05h 37m 26.26s , -04d 45m 21.1s) |   C |    60 | 18.3 |        
   23236 | 2025-09-03 01:12:19 |         MASTER-SAAO | (05h 28m 47.39s , -06d 25m 15.1s) |   C |    60 | 17.9 |        
   23236 | 2025-09-03 01:12:19 |         MASTER-SAAO | (05h 30m 35.79s , -06d 40m 38.5s) |   C |    60 | 17.9 |        
   23329 | 2025-09-03 01:13:52 |         MASTER-SAAO | (05h 36m 43.44s , -06d 25m 56.1s) |   C |    60 | 18.5 |        
   23329 | 2025-09-03 01:13:52 |         MASTER-SAAO | (05h 38m 31.77s , -06d 41m 19.5s) |   C |    60 | 18.6 |        
   23422 | 2025-09-03 01:15:26 |         MASTER-SAAO | (05h 29m 30.58s , -04d 47m 30.8s) |   C |    60 | 18.0 |        
Filter C is a clear (unfiltred) band. 


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