GCN Circular 40934

J.X Cao (GXU), Y.H Cheng (SWIFAR, YNU), W.J Xie (NAOC), D.H Zhao (NAOC), N. Dagoneau (CEA), L. Zhang (IHEP), C. Van Hove (IJCLab), P. Maggi (ObAS) report on behalf of the SVOM mission team: 

At 2025-07-04T03:42:22 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 250704A (SVOM burst-id sb25070404).

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 11 alerts. CRT provided the alert with the best signal-to-noise-ratio (SNR) in the image of 11.88 in the [8-120] keV energy band over a time window of 5.10 seconds starting at 2025-07-04T03:42:20.

The localization of the best alert is R.A., Dec. 17.1325, -17.2798 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.78 arcmin (including systematic error of 2 arcmin added in quadrature).

This burst also triggered SVOM/GRM at 2025-07-04T03:42:20 with a SNR of 9.20. The SVOM/GRM light curve showed a single peak structure with a duration of about 8 seconds.
The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb250704A.png.

SVOM/MXT began observing the field at 2025-07-04T03:45:35 UTC, 192 seconds after T0. Using data rapidly transmitted to the ground via the VHF network, we found an uncatalogued X-ray source located at R.A., Dec. 17.1760, -17.3394 degrees:
R.A. (J2000) = 1h08m42.24s
Dec. (J2000) = -17d20m21.8s
with a 90% C.L. radius of 102 arcseconds (including a systematic uncertainty of 35 arcseconds added in quadrature).

This location is 4.36 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received in the full X-band dataset.

VT began observing the field after the slew. The analysis of the data will be published in a future circular.

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 Jiaxin Cao: cjx@st.gxu.edu.cn.
Please contact the BA by email if you require additional information.