TITLE:   GCN CIRCULAR
NUMBER:  43633
SUBJECT: GRB 260207A : MASTER optical counterpart discovery
DATE:    26/02/07 19:42:05 GMT
FROM:    Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>

C. Francile (OAFA), O.Gress (ISU), V.M.Lipunov (Lomonosov MSU), R.Podesta, F.Podesta (OAFA),
D.Svinkin, A.Ridnaya (Ioffe Institute),
I.Panchenko, P.Balanutsa, G.Antipov, A.Kuznetsov, E.Gorbovskoy, N. Tiurina, Ya.Kechin,A.Chasovnikov,
V.A.Senik, D.Vlasenko, I.Ionov,Yu.Tselik(Lomonosov MSU),
N.Budnev, R.Mirgazov, A.Diachok, O.Ershova (Irkutsk State University),
E. Gonzalez (OAFA, San JuanUni.,Argentina);
D.Buckley (SAAO),
A. Sosnovskij (CrAO RAS),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella, J.G.
Tanori,  L. F. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro AstrophysicObservatory, Mexico)
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain)

MASTER Global Robotic Net started (Lipunov et al. GCN 43627) Fermi GRB 260207A (GCN 43628)
alert observtions at MASTER-OAFA 110 sec after notice time and 142 sec after trigger time at 2026-02-07 05:44:56 UT

MASTER OT J104411.31-330936.2 discovery

MASTER-OAFA auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L )
 discovered OT source at (RA, Dec) = 10h 44m 11.31s -33d 09m 36.2s on 2026-02-07.24049 UT.

The OT unfiltered  magnitude was 17.3m(mlim19.8=).

The OT is seen in 27 images with typical decay with different features at light curves.

 There is no minor planet at this place.

We have reference image on 2025-02-08.36365 UT with unfiltered 20.1m.
Deep photometry and spectral observations are required.

We reobserved these coordinates at MASTER-SAAO at 2026-02-07 18:59:00 without object, that confirmed GRB optical counterpart nature