TITLE: GCN CIRCULAR NUMBER: 42180 SUBJECT: SVOM/sb25101004: SVOM detection of a stellar flare DATE: 25/10/10 07:23:03 GMT FROM: SVOM_group svomgroup@bao.ac.cn

Donghua ZHAO, Chao Wu, Wenjin Xie (NAOC), Hatsunegoto Goto(Kanazawa Univ./CEA)，Florent Robinet (IJCLab), Nicolas Dagoneau, J. T. Palmerio (CEA) report on behalf of the SVOM mission team

At 2025-10-10T03:51:58 UTC (T0), SVOM/ECLAIRs triggered and located the source (SVOM burst-id sb25101004).

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

The source was only detected by the Image Trigger (IMT), which produced a sequence of 5 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 9.82 in the [5-20] keV energy band over a time window of 327.68 seconds starting at 2025-10-10T03:47:53.

The localization of the best alert is R.A., Dec.: 311.3214, -31.4119 degrees (J2000) with a 90% confidence level (C.L.) radius of 8.10 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the source.

SVOM/MXT began observing the field at 2025-10-10T04:00:23 UTC, 505 seconds after T0. Using X band data we found a source located at R.A., Dec.: 311.2972, -31.3445 degrees: R.A. (J2000) = 20h45m11.338s Dec. (J2000) = -31d20m40.213s with a 90% C.L. radius of 25.8 arcseconds (including a systematic error of 25 arcsec added in quadrature).

This location is 4.23 arcminutes from the ECLAIRs onboard position. No uncatalogued fading X-ray counterpart was detected.

There is a known source HD 197481 (Au Mic: a young red dwarf star ) which is 4.23 arcmin away from ECLAIRs position and is 26 arcsec away from MXT position. These results show that this trigger is probably caused by the stellar flare of HD 197481 (Au Mic).

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 Donghua Zhao: zhaodh@bao.ac.cn. Please contact the BA by email if you require additional information.

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