GCN Circular 40014

X. Chen(YNU), Y. Hu(GXU), H. Yang(IRAP), B. Cordier (CEA), L. Zhang(IHEP), P. Maggi (ObAS)
on behalf of the SVOM mission team.

At 2025-04-02T23:07:56 UTC (Tb) SVOM/ECLAIRs triggered on the gamma-ray burst GRB 250402A (SVOM burst-id sb25040203).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 15 alerts. IMT provided the alert with the best signal-to-noise-ratio (SNR) of 27.79 in the [8-120] keV energy band over a time window of 40.96 seconds starting at Tb.
The light curve showed a long GRB with a T90 duration of about 35 (+/-3) s.

The localization of the best alert is R.A., Dec 213.3783, -5.9457 degrees (J2000) with a 90% C.L. radius of 3.42 arcmin (including systematic error of 2 arcmin added in quadrature).

SVOM slewed to the burst.

MXT began observing the field at 2025-04-02T23:10:58 UTC, 183 seconds after Tb.

Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec 213.3893, -5.9468 degrees:
RA (J2000) = 14h13m33.44s
DEC (J2000) = -5d56m48.59s
with a 90% C.L. radius of 45 arcseconds(including 25 arcseconds systematic error added in quadrature).
This location is 0.66 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

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 X. Chen: xlchen@stu.ynu.edu.cn.
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.