TITLE: GCN CIRCULAR NUMBER: 40287 SUBJECT: SVOM/sb25043004: SVOM detection of a X-ray transient DATE: 25/04/30 11:39:06 GMT FROM: SVOM_group svomgroup@bao.ac.cn

Y. Liang (PMO), W. Zheng (Berkeley), O. Godet, S. Guillot (IRAP), C. Plasse, J. T. Palmerio (CEA) on behalf of the SVOM mission team.

SVOM/ECLAIRs triggered and located the X-ray transient sb25043004 (SVOM burst-id sb25043004) starting at 2025-04-30T10:40:57.1 UTC (Tb).

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 3 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 8.96 in the [5-8] keV energy band over a time window of 327.68 seconds starting at Tb.

The localization of the best alert is R.A., Dec. 272.104, -38.6635 degrees: R.A. (J2000) = 18h08m25.13s Dec. (J2000) = -38d39m48.60s with a 90% confidence level (C.L.) radius of 8.82 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the source.

MXT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.

VT began observing the field after the slew. The analysis of the recorded images will be published in a future circular gathering information on the follow-up of the SVOM optical instruments.

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 Weikang Zheng: weikang@berkeley.edu. Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.

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