sb25090605

M. G. Bernardini (INAF, LUPM), M. Gnaoui (IAP), S. Schanne, N. Dagoneau (CEA/Irfu), F. Piron (LUPM), M. Moita (CEA/Irfu)

At 2025-09-06T21:18:30 UTC (T0), SVOM/ECLAIRs triggered and located an X-ray transient (SVOM burst-id sb25090605) from the LMXB 4U 0513-40, which is not present in the trigger onboard catalog.

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

The source was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 11 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 14.14 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2025-09-06T21:18:25.

The localization of the best alert is R.A., Dec. 78.5709, -40.0751 degrees (J2000) with a 90% confidence level (C.L.) radius of 5.8 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the source.

SVOM/MXT began observing the field at 2025-09-06T21:21:09 UTC, 159 seconds after T0. Using onboard processed data we found an X-ray source located at R.A., Dec. 78.5386, -40.0520 degrees:
R.A. (J2000) = 5h14m09.26s
Dec. (J2000) = -40d03m07.30s
with a 90% C.L. radius of 50 arcseconds (including systematic error). 

This location is 2 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

The MXT position is consistent with the position of LMXB 4U 0513-40, located at 44 arcseconds.

VT began observing the field after the slew.

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 Maria Grazia Bernardini: maria.bernardini@inaf.it.
Please contact the BA by email if you require additional information.