TITLE: GCN CIRCULAR NUMBER: 39065 SUBJECT: Swift GRB250129.20: Global MASTER-Net OT detection DATE: 25/01/29 05:08:46 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs lipunov@xray.sai.msu.ru

C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), V.Lipunov, E.Gorbovskoy, N.Tiurina, P.Balanutsa, D.Vlasenko, I.Panchenko, A.Kuznetsov, G.Antipov, A.Sankovich, A.Sosnovskij, Yu.Tselik, M.Gulyaev, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina (Lomonosov MSU), O.Gress, N.Budnev(ISU), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), 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 (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) was pointed to the GRB250129.20 162 sec after notice time and 240 sec after trigger time at 2025-01-29 04:49:09 UT. On our second (60s exposure) set , obtained 296 sec after tigger time at 2025-01-29 04:50:05 UT, we found 1 optical transient within Swift error-box (ra=198.683 dec=5.03833 r=0.05) brighter than 18.3.

T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 326 2025-01-29 04:50:05 60 (13h 14m 42.38s , +05d 01m 50.1s) 17.5

The 5-sigma upper limit has been about 18.3mag The message may be cited.

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