TITLE: GCN CIRCULAR NUMBER: 39955 SUBJECT: SVOM/sb25033102: SVOM detection of an X-ray transient DATE: 25/03/31 03:40:23 GMT FROM: SVOM_group svomgroup@bao.ac.cn

Yinuo MA, Chao WU, Donghua ZHAO, Wenjin XIE (NAOC), Hatsune GOTO (CEA, Kanazawa Univ) on behalf of the SVOM mission team.

At 2025-03-31T02:04:18 UTC (Tb) SVOM/ECLAIRs triggered on the X-ray transient labelled sb25033102 (SVOM burst-id sb25033102). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

This transient was only detected by the Count-Rate Trigger (CRT), which produced a sequence of 1 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 15.10 in the [8-120] keV energy band over a time window of 20.48 seconds starting at Tb.

The localization of the best alert is R.A., Dec 289.235, -18.527 degrees: RA (J2000) = 19h16m56.51s Dec (J2000) = -18d31m37.10s with a 90% C.L. radius of 5.48 arcmin (including systematic error of 2 arcmin added in quadrature).

We notice that this transient also triggered SVOM/ECLAIRs at the 1.57 hours before, at 2025-03-31T00:29:51.04 (SVOM/sb25033101). Due to an external ToO was performing by SVOM, no immediate slew was performed on this transient.

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.

The Burst Advocate (BA) on shift for this burst is Yinuo MA: mayn@bao.ac.cn Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.

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