sb25091517

H.L. Li (NAOC), L.P. Xin, Y. N. Ma,  Y.L. Qiu, C. Wu, Z.H. Yao, X.H. Han, J. Wang, W.J. Xie, Y. Xu, H.B. Cai, J.Y. Wei (NAOC), J. Palmerio (CEA), Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester) report on behalf of the SVOM team.

SVOM performed an automatic slew on the soft burst triggered by SVOM/ECLAIRs (Julakanti et al., GCN 41834
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 ) in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. The observation with good image quality began at 2025-09-15T22:09:18, i.e., 457 sec post trigger. 
 
With X band downlinked data, preliminary analysis shows that the M2 dwarf 1RXS J020013.6-084106 located within MXT's errorbox (Julakanti et al., GCN 41834
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 ) was decreasing in brightness from 10.6 mag to 12.2 mag in VT_B during 3 hour time interval after the trigger time. This result confirms that the trigger was due to a stellar flare, as already reported by Jelinek et al. (GCN 41617
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 ). Our photometry was estimated in AB magnitude. 

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.

Martin Jelinek, Jan Strobl (ASU CAS Ondrejov, CZ),
Sergey Karpov, Martin Masek, Petr Janecek, Jakub Jurysek,
Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza
(Institute of Physics, Prague, CZ)

report:

The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted
robotically to the alert of SVOM/sb25091517 (Julakanti et al. GCN
41834
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 ), obtaining a series of 70 x 60s unfiltered images starting at
22:51 UT, i.e. 50 min post trigger.

We clearly detect the high proper motion star 1RXS J020013.6-084106 at
coordinates R.A. = 02:00:12.98, Dec. = -08:40:53.5 (J2000), located 18
arcsec from the MXT position as noted in the discovery circular. The
star shows a decay from unfiltered magnitude ~11.0 to ~11.4 over our
80-minute observing sequence ending at 00:11 UT, with one brief 0.1 mag
rebrightening episode during the observations.

The observed photometric behavior is consistent with the stellar flaring
nature suggested in the discovery circular.

Y. Julakanti, R. A. J. Eyles-Ferris (U. Leicester), S. Schanne (CEA/Irfu), F. Piron (LUPM), H. Goto (Kanazawa Univ./CEA), report on behalf of the SVOM mission team:

At 2025-09-15T22:01:41 UTC (T0), SVOM/ECLAIRs triggered and located the X-ray transient SVOM/sb25091517 (SVOM burst-id).

The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

The burst was only detected by the Image Trigger (IMT), which produced a sequence of 3 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 8.81 in the [5-20] keV energy band over a time window of 655.36 seconds starting at 2025-09-15T21:56:13 (Tb).

The localization of the best alert is R.A., Dec. 30.1388, -8.7614 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.96 arcmin (including systematic error of 2 arcmin added in quadrature). We notice the presence of the known X-ray sources 6dFGS gJ020039.1-084555, 2E 0157.9-0853, 1RXS J020013.6-084106, CXOMP J020012.1-085113 in the ECLAIRs error box.

SVOM slewed to the burst.

SVOM/MXT began observing the field at 2025-09-15T22:09:15 UTC, 454 seconds after T0. Using onboard processed data we found an X-ray source located at R.A., Dec. 30.0581, -8.6826 degrees:
R.A. (J2000) = 2h00m13.94s
Dec. (J2000) = -8d40m57.37s
with a 90% C.L. radius of 30 arcseconds.
This location is 6.73 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

We notice that the High Proper Motion Star 1RXS J020013.6-084106 is located at 18 arcsec from the MXT position. Therefore this trigger is likely caused by a flare from this star.

VT began observing the field after the slew. The analysis of the data will be published in a future circular.

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.

The Burst Advocate (BA) on shift for this alert is Yashaswi Julakanti: skyj1@leicester.ac.uk.
Please contact the BA by email if you require additional information.