TITLE: GCN CIRCULAR NUMBER: 41622 SUBJECT: IceCube Alert 250831.75: Global MASTER-Net observations report DATE: 25/09/01 00:39:34 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) was pointed to the IceCube Alert 250831.75 (trigger No 5972385,07h 02m 33.60s , +05d 02m 24.0s, R=0.53) errorbox 20982 sec after notice time and 21045 sec after trigger time at 2025-08-31 23:51:31 UT, with upper limit up to 17.3 mag. The observations began at zenith distance = 83 deg. The sun altitude is -26.9 deg.

The galactic latitude b = 5 deg., longitude l = 210 deg.

Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=2980982

We obtain a following upper limits.

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

21075 | 2025-08-31 23:51:31 | MASTER-Kislovodsk | (07h 00m 41.24s , +05d 07m 13.0s) | C | 60 | 15.9 | 21135 | 2025-08-31 23:51:31 | MASTER-Kislovodsk | (07h 00m 41.26s , +05d 07m 12.7s) | C | 180 | 16.4 | Coadd 21075 | 2025-08-31 23:51:31 | MASTER-Kislovodsk | (07h 00m 37.35s , +04d 44m 38.4s) | C | 60 | 15.9 | 21155 | 2025-08-31 23:52:51 | MASTER-Kislovodsk | (07h 00m 43.33s , +05d 08m 51.7s) | C | 60 | 15.8 | 21155 | 2025-08-31 23:52:51 | MASTER-Kislovodsk | (07h 00m 39.47s , +04d 46m 16.8s) | C | 60 | 15.8 | 21235 | 2025-08-31 23:54:11 | MASTER-Kislovodsk | (07h 00m 38.32s , +05d 08m 20.3s) | C | 60 | 15.7 | 21235 | 2025-08-31 23:54:11 | MASTER-Kislovodsk | (07h 00m 34.57s , +04d 45m 45.1s) | C | 60 | 15.9 | 21315 | 2025-08-31 23:55:31 | MASTER-Kislovodsk | (07h 00m 37.37s , +05d 09m 24.8s) | C | 60 | 15.9 | 21375 | 2025-08-31 23:55:31 | MASTER-Kislovodsk | (07h 00m 37.37s , +05d 09m 24.7s) | C | 180 | 16.4 | Coadd 21315 | 2025-08-31 23:55:31 | MASTER-Kislovodsk | (07h 00m 33.70s , +04d 46m 50.1s) | C | 60 | 16.0 | 21395 | 2025-08-31 23:56:50 | MASTER-Kislovodsk | (07h 00m 44.34s , +05d 08m 27.2s) | C | 60 | 15.9 | 21395 | 2025-08-31 23:56:50 | MASTER-Kislovodsk | (07h 00m 40.78s , +04d 45m 52.4s) | C | 60 | 15.9 | 21474 | 2025-08-31 23:58:10 | MASTER-Kislovodsk | (07h 00m 39.37s , +05d 07m 32.4s) | C | 60 | 16.0 | 21475 | 2025-08-31 23:58:10 | MASTER-Kislovodsk | (07h 00m 35.89s , +04d 44m 57.5s) | C | 60 | 16.0 | 22440 | 2025-09-01 00:13:15 | MASTER-Kislovodsk | (07h 00m 37.64s , +05d 10m 27.0s) | C | 180 | 17.1 | 22440 | 2025-09-01 00:13:15 | MASTER-Kislovodsk | (07h 00m 39.06s , +04d 47m 32.5s) | C | 180 | 17.3 | 23039 | 2025-09-01 00:23:14 | MASTER-Kislovodsk | (07h 00m 37.10s , +04d 48m 25.8s) | C | 180 | 17.0 | 23039 | 2025-09-01 00:23:14 | MASTER-Kislovodsk | (07h 00m 38.51s , +05d 11m 07.6s) | C | 180 | 16.9 | Filter C is a clear (unfiltred) band.

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

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