TITLE:   GCN CIRCULAR
NUMBER:  39735
SUBJECT: GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi  detection
DATE:    25/03/15 14:28:50 GMT
FROM:    Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>


Ya.Kechin, V.Lipunov,N.Tyurina, E.Gorbovskoy, A.Kuznetsov, G.Antipov, D.Vlasenko,K.Zhirkov, P.Balanutsa,
A.Chasovnikov, V.Topolev, V.Senik, K.Labzina (Lomonosov MSU),
D.Buckley (SAAO),
C.Francile,  F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A.Sosnovskij (Crao RAS),
O.Gress, N.Budnev, O.Ershova (ISU),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
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 AstrophysicsObservatory)


MASTER Global Robotic Net (Lipunov, Kornilov, Gorbovskoy, Tiurina & Kuznetsov, 2023, Astronomical Robotic Networks and
Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp, http://www.pereplet.ru/lipunov/625.html#625)
started observation  GRB 250313.89 (trigger 763594063, Ttrigger= 2025-03-13  21:27:38.85UT center (14h 43m 16.01s , -45d 40m 00.1s, radius=8.4167deg;
https://master.sai.msu.ru/site/master2/event.php?id=2811407  )
at 2025-03-14 07:26:28 (OAFA, Argentina) and 2025-03-14 23:24:55 (SAAO,
South Africa).

Cover map is available at
https://master3.sai.msu.ru:444/static/png/GRB250313.89/FERMI//1107805802.png.1.png

MASTER OT J150644.86-414140.4 (AT 2025ehi)  detection inside 1 sigma errobox.


MASTER-OAFA auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L )
 discovered OT source at (RA, Dec) = 15h 06m 44.86s -41d 41m 40.4s on 2025-03-14.20999 UT.

The OT magnitude in 'Clear' filter is 16.0m
(mlim = 18.9).

The OT is seen in 38 images.
We see the growing light  curve of shine up to 13 zyading values ​​within 1 day.
There is no minor planet at this place.

We have reference image on 2025-03-02.26325 UT with 'Clear' filter 19.9m.
There is the  Guide Star Catalog object 22 magnitude  at same position.
Spectral observations are required.