TITLE: GCN CIRCULAR NUMBER: 42211 SUBJECT: GRB 251011B inspection: MASTER orphan GRB detection DATE: 25/10/13 00:15:06 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru> Ya.Kechin, V.Lipunov, P.Balanutsa, A.Kuznetsov, G.Antipov, I.Panchenko, K.Zhirkov, E.Gorbovskoy, N.Tiurina, A.Sankovich, Ya.Kechin, M.Shilova, A.Chasovnikov, V.Topolev, V.Senik, D.Vlasenko, Yu.Tselik (Lomonosov MSU), R.Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San Juan Uni.,Argentina); D.Buckley, (SAAO, South Africa) O.Gress, N.Budnev (ISU, Irkutsk), A. Sosnovskiy (CrAO RAS), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico) The MASTER-OAFA robotic telescope of the MASTER Global Robotic Net [1,2,3,4] started Swift GRB 251011B (Ttrigger=2025-10-11 07:08:22UT; XRT RA,Dec(2000)=00h 52m 56.33s,-62d 02'00.2" GCN 42197, GCN 42201) alert observations at 2025-10-11 07:09:27 and observed it up to sunrise (Balanutsa et al. GCN 42203). Next night MASTER automatic planner continued Fermi error-box (GCN 32196) inspection as independent alert MASTER OT J011025.98-583210.6 discovery MASTER-OAFA auto-detection system of MASTER Global Robotic Net [1,2,3,4] during Fermi GRB 251011B (GCN42204, also detected by Swift (GCN42197) and observed by MASTER in alert mode (GCN 42203)) inspection discovered OT source at (RA, Dec) = 01h 10m 25.98s -58d 32m 10.6s on 2025-10-12.16208 UT with light curve, that is typical for gamma-ray bursts optical counterpart. The OT unfiltered magnitud m=17.8 (first image) at 2025-10-12 03:53:24UT (mlim=19.3 at single image). The OT is seen in 8 images with typical GRB counterpart decay. There is no minor planet at this place. We have reference image on 2025-09-16.19346 UT with unfiltered mlim=20.3m. So as the Ttrigger for GRB 251011B was 19h earlier our discovery time (2025-10-11 07:08:22.33UT) and Swift error-box center was at 00h 52m 56.33s -62d 02' 00.2" (Swift GCN 42197, GCN 42201) MASTER OT looks not connected with just GRB 251011B, but can be the orphan one [5]. Spectral observations and deep photometry are required. [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov V., Kornilov V., Gorbovskoy E., Tiurina N., Kuznetsov A. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 [5] Lipunov et al. 2022, MNRAS, 516, 4980 https://ui.adsabs.harvard.edu/abs/2022MNRAS.516.4980L/abstract View this GCN Circular online at https://gcn.nasa.gov/circulars/42211. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...