GCN Circular 40576

Y. Wang (PMO, CAS), J.X Cao (GXU), D. Turpin (CEA), M. G. Bernardini (INAF-OAB, LUPM), D. Götz (CEA), C. Plasse (CEA), L. Zhang (IHEP) on behalf of the SVOM mission team.

SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250530A (SVOM burst-id sb25053002) starting at 2025-05-30T06:31:54.99 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 both the Count Rate Trigger (CRT) and  the Image Trigger (IMT). A sequence of 11 alerts was produced. CRT provided the alert with the best signal-to-noise-ratio (SNR) of 9.50 in the 8-50 keV energy band over a time window of 20.40 seconds starting at Tb.

The localization of the best alert is R.A., Dec. 186.71, -2.5648 degrees:
R.A. (J2000) = 12h26m50.37s
Dec. (J2000) = -02d33m53.38s
with a 90% confidence level (C.L.) radius of 8.35 arcmin (including systematic error of 2 arcmin added in quadrature).

The ECLAIRs light curve showed a multiple peak structure with a T90 duration of about 7.57 (-4.98 +2.48).

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250530A.png

SVOM slewed to the burst.

MXT began observing the field after the slew. The onboard software did not detect any x-ray source in the ECLAIRs error region. Further analysis of MXT data will be published in a future circular.

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 Y. Wang: wangyun@pmo.ac.cn.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.