GCN Circular 39398

R.-Z. Li (YNAO, CAS), Y. Wang (PMO, CAS), J.-X. Cao, D.-F. Kong (GXU), W.-J. Xie, D.-H. Zhao (NAOC), M. Moita (CEA), L. Zhang (IHEP) report on behalf of the SVOM mission team:

The SVOM/ECLAIRs telescope triggered and located a soft X-ray transient (SVOM burst-id sb25022102) starting at 2025-02-21T02:57:58.938 UTC (Tb).

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

The burst was detected by the Count-Rate Trigger (CRT) mode and 2 alerts were produced with a best signal-to-noise ratio of 9.66 in the 8-120 keV energy band over a time window of 20.48 second starting at Tb. 

The localization of the alert is R.A., Dec = 231.472, -17.950 degrees:
RA (J2000) = 15:25:53.18
Dec (J2000) = -17:56:58.32
with a 90% C.L. radius of 8.22 arcmin (including systematic error of 2 arcmin added in quadrature).

We notice that this error-box contains an X-ray source which could produce such a transient, which is 1RXS J152553.0-174943 in Simbad, located at 7.3 arcmin distance.

The SVOM/GRM lightcurve could be find the link below:
https://www.bursthub.cn//admin/static/svgrb20250221A.png

This trigger reached the slew threshold, hence automatic slew was performed. No X-ray sources were found in the VHF data of SVOM/MXT at 1.22 hours after the trigger. A SVOM ToO has been scheduled.

The Space 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 R.-Z. Li (YNAO, CAS): 
liruizhi@ynao.ac.cn
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.